Does Buddhism apply to this formula for Christianity?

That is certainly the formula for Christianity. Christianity is a mental virus. Adaptations that help it infect new hosts, or keep the host from leaving (being cured) are propagated into the next generation. Any mutations that set a host free, would have to set them free of Christianity too, so such mutations aren't evolutionarily advantageous.

All religions are susceptible to this kind of value drift. However, Buddhism has some characteristics that keep it purer:

• The idea that Buddhism is just a vehicle, to be discarded the moment the journey is complete, is explicitly included in Buddhism. Buddhism is designed to be abandoned when its usefulness is over. The same can't be said for Christianity. To a Christian, the idea of them becoming enlightened (exactly like Jesus) is offensive.
• There is a written record of a lot of things Buddha said, that has been preserved far better than what Jesus said. The New Testament is a set of stories mostly written by people who had never met him, then copied and edited, bits added or taken away depending on the preferences of the copier, and at some point any writings that weren't consistent with what the people in charge wanted it to say, were destroyed and made illegal.

Some religions offer an end to suffering only after death, in heaven, provided that you're a believer and have fulfilled the requirements of those religions.

But in Buddhism, when you look deep into the original teachings of the Buddha, he provided methods to reduce sufferings in the here and now, even for a lay person, who is not a professional full time practitioner of the Noble Eightfold Path.

By adopting the five precepts, Right Speech, Right Action and Right Livelihood, and changing his thoughts in such a away that he takes responsibility for his future actions, and detaches himself emotionally from things out of his control, a Buddhist, even a lay Buddhist, can reduce his sufferings in the here and now.

The idea is that if you cling to things that are out of your control, and those things change because they are impermanent, then this will cause you to suffer. If you cling to the past, that you cannot change, then it will also make you suffer. Also, for things that are in your control (i.e. future thoughts, words and actions), if you behave unvirtuously, then it will also cause you to suffer.

Understanding this, a Buddhist can change his thoughts and behavior in such a way that he can reduce his suffering.

In other words, a Buddhist doesn't even have to be a stream enterer to experience a significant reduction in suffering.

From the conversation you had with your brother I assume(may be wrong assumption) he is agnostic. He seems to have a strong sense of attachment to life. Maybe he is not yet seeing the vicissitudes of life. Every one of us is wired with innate ignorance and it is easy to have a blind eye to the suffering that is happening all around.And also it is extremely hard to understand that ignorance is at the root of our suffering. By suffering here i mean the ever perceived gap between what is and what should be(I guess this includes every form of suffering).

If he is of the type who doesn't see the suffering enough yet, give him a gap to see the suffering by himself or if you can point him to how dissatisfaction, insecurity and conflict are prevalent in every walk of human life.

If he is of the type who sees the suffering but doesn't think there is any escape from it, you can point him how Buddhism can help to end suffering by clearly making us to understand the root cause of suffering and showing us the method to fix the cause there by freeing us from suffering, right now in the present life.

What use is of promise that is only fulfilled after death ?

If I may suggest, compassion and love should be the motive during our discussions with fellow human beings, not the desire to be right always.

Hatred is never appeased by hatred in this world. By non-hatred alone is hatred appeased. This is a law eternal -Dhammapada

I feel here hatred is not just simple hatred but hatred in many subtle forms like our desire to be right, our desire to despise other points of view, jealousy, competitiveness and antagonism etc.

life is bad, but we can end suffering in some distant end goal

It may sound facile, but if the cause of suffering is craving, then acknowledging that, and finding a means to end craving, would be a special way overcome "suffering".

https://en.wikipedia.org/wiki/Four_Noble_Truths

However, if suffering just means "life is bad", rather than life being endless rebirths into conditioned existence, then Buddhism may not be a very helpful counteraction - even if it is a "moral" one.

Because, as you say, few can be Buddhas in this life.

Your brother projects his own definition of suffering onto Buddhism.

I've read that the Buddha said something close to this:

"There are these three kinds of suffering [dukkhata]. What three? Suffering which is pain & misery [dukkhadukkhata], suffering which is the formations [sankharadukkhata], suffering associated with change [viparinamadukkhata].

These three feelings have been spoken of by me: a feeling of pleasure, a feeling of pain, & a feeling of neither pleasure nor pain. These are the three feelings spoken of by me. But I have also said: 'Whatever is felt comes under stress.' That I have stated simply in connection with the inconstancy of fabrications. That I have stated simply in connection with the nature of fabrications to end... in connection with the nature of fabrications to fall away... to fade away... to cease... in connection with the nature of fabrications to change.

"And I have also taught the step-by-step cessation of fabrications.

Now it's possible, Ananda, that some wanderers of other persuasions might say, 'Gotama the contemplative speaks of the cessation of perception & feeling and yet describes it as pleasure. What is this? How can this be?' When they say that, they are to be told, 'It's not the case, friends, that the Blessed One describes only pleasant feeling as included under pleasure. Wherever pleasure is found, in whatever terms, the Blessed One describes it as pleasure.'"

Ven. Udayin said to Ven. Sariputta, "But what is the pleasure here, my friend, where there is nothing felt?"

"Just that is the pleasure here, my friend: where there is nothing felt.

Suffering is defined differently in these religions and therefore the goals are entirely different.

Nowhere does Islam define perception, congnizance, feelings, sensations, ideas, intentions, attention, mind or intellect as suffering; and nowhere do they speak of an altogether extinguishment of the conditioned as 'the unconditioned' and define the extinguishment as primary principal bliss, which is spoken of as antonymic to suffering in a definitive sense.

As a matter of fact these systems of thought aren't in agreement as to what consciousness is and understand the concept of feelings & perception differently.

They aren't in agreement as to what suffering is and as to what is & isn't possible. The goals are antagonistic.

If the goals are entirely different then it's foolish to say "the goal is the same and they all fall short of the goal".

I like Stephen Batchelor's emphasis on the four noble truths as to be actively realised, rather than to be taken as dogmatic declarations. He adds the verbs I've italicised:

understand There is suffering (or anguish, or unsatisfactoriness) (& it's one of the three marks of existence)

realise There are causes of suffering

giving up (attachments that cause suffering shows us ) There is a path to the cessation of suffering

develop (using) The path to the cessation of suffering which is Buddhism and the Eightfold Path (which can be seen as like a 'stock take', working through attention to different aspects of our life, like speech, or livelihood, and applying the previous : understand, realise, give up, develop ; about what we know causes suffering in each area)

So I see it not as a distant goal, but an active process, yo bring into our lives. Through developing meditative concentration, and mindfulness, we witness where suffering is, we try to understand it's causes, we try to change things and let go of the parts of ourselves which contribute to causing suffering. And the Eightfold Path helps us keep balance with our attention, on to different aspects of our lives.

This focus on the personal, the taking responsibility for our reactions to the world, is just like stoicism, in mood, stepping away from being coerced by others & ourselves. But, Buddhism goes further. It says holding to these truths, this path, can take us to a different way to be, a way not premised on attachment, and suffering that follows 'like the wheel follows the ox'. A way that is to our ordinary way, like being awake is to being asleep. Unshakeable liberation, from causing suffering.

That still hasn't ended suffering. Not being a cause of suffering, does not end suffering in the world. That is where the bodhisattva path is needed, to save all sentient beings from suffering. And that, is a distant goal. But a long journey, begins with a little step.

This question deals with soteriology — the theory of salvation advocated by a religion or philosophy — and soteriology is never quite as simple and straightforward as one might like. We can discuss the differences in soteriology between Buddhist and Abrahamic worldviews. But if we do we have to recognize that mystical sects interpret soteriological principles differently from liturgical sects, and those differences can be significant.

As a general rule, liturgical sects present salvation as a sort of transaction: obedience to doctrinal principles in the present make one welcome into a state of salvation sometime in the future. Christians, thus, hold out the promise of heaven after death for those faithful who adhere to the commandments and teachings; Liturgical Buddhists, by contrast, envision a series of rebirths, where those dedicated to the teachings of the Buddha use 'right' behavior to slowly relive themselves of of past misdeeds, working their way up to ultimate salvation-through-release of the nirvana. Liturgical practices are often comforting and effective for those spiritually at sea; who need structure and guidance to lead them to proper understanding.

Mystical sects tend to remove the temporal element: to take the idea of salvation out of the (distant) future and re-construe it as an ever-present state which one merely needs to access, touch, or remember. Christian mystics tend to follow Luke 17:21 and the idea that the Kingdom of God is already among or within us; Mystical Buddhists tend to emphasize the immediacy of the state of enlightenment, which exists beneath and around and within the attachments that cover it.

It is often the case that people outgrow liturgical worldviews before they have properly grown into a mystical worldview. For such people, liturgical practices will start to seem 'phony' or 'strained', and the entire project of religion feels bankrupt. Some people reach that stage and collapse into a sour nihilism; your friend's statement is a typical expression of that. Other people retreat into confusion or agnosticism, perhaps clinging to the form of the faith without really believing it. A few go through a rough patch and transcend, returning with a more mystical outlook and a different relationship to the practices and tenets of the faith.

If you're friend's sourness has shaken your worldview a bit, that's fine. Worldviews need to be shaken every once in a while or we fall into complacency. But don't doubt the reality of the teaching. Instead, re-examine your relationship to the teaching. It will come into balance.

Buddhism has diagnosed all suffering as possessive attachment to the five components of life (body, feelings, perception, mental formations & consciousness) as 'self'.

Buddhism has also diagnosed the primary cause or fuel behind this attachment is craving.

Therefore, ask your brother: "Can suffering exist without self-attachment & craving?"

Then ask your brother: "If there was no craving & no self-attachment, would suffering end?"

For example, ask your brother would he suffer if my computer was stolen? Then ask your brother would he suffer if his computer (or another object he cherished) was stolen? The expected answer to this question proves the suffering is due to self-attachment; that he would not suffer about my lost computer but would suffering about his lost computer.

Then ask your brother: "Does the suffering occur because he desires/craves to have his computer and he desires to not have to spend money on a new computer?" The expected answer to this question proves the suffering & attachment is caused by craving.

Then ask your brother if he completed believed the computer was "not-self" ("anatta"), like the Enlightened Buddhists completely believe, would he suffer over a disappearing computer?

This shows Buddhist enlightenment works to end suffering.

he would probably say, "how can you prove that craving and attachment can come to an end?" I have to guess at what he would say because he's no longer willing to have this conversation

Say to him: "Imagine you saw, from a distance, a beautiful looking lady with long blonde hair dressed in a red bikini walking towards you. Then as the lady came close to you and took off her bikini and blonde wig, it was revealed the lady was really a man dressed as a woman". Would your desire end?

Or imagine he is given a hot nice garlic smelling pizza box but when he opens the pizza box, it is full of dog shit. Would his desire end?

The examples show desire can end.

Or another example: say he was offered cheap wine to drink but then was offered very expensive wine to drink. Would his desire towards the cheap wine end? Similarly, when a meditator enters the heavenly meditation state called "jhana", because pleasure in that heavenly state is far better than the pleasure of sensual objects, the desire towards sensual objects end. This shows desire can end.

For me, the Buddha’s great insight about suffering had a very practical goal in this life—not some future one. I see this goal being confused with the accomplishment of the enlightenment and total realization of the Buddha. That takes much time and patient dedication which I won’t speak about.

I feel that it is important to point out a couple of obvious differences between Christianity and Islam, and what came to be called Buddhism: the Buddha was not God and is not the creator, and the point of Buddhism is not to worship Buddha, but to emulate him throughout your life, while practicing what he taught about ending suffering. The desire to end suffering does not bring about ‘happiness’. That is the well-crafted carrot on a stick that consumptive corporatists dangle in front of us to keep us wanting more and more in a hopeless chase to find something which ultimately can’t be found outside ourselves.

The Buddha’s path doesn’t make you happy, although you might experience being happy while on that path; instead, the Buddha taught how to end suffering, which leads to the satisfaction called comfort. All too often today, that message is corrupted, by those that should know better, into a ‘buddhist’ search for ‘happiness.’

The goal to be sought is not momentary elation, but an enduring, universal omnipresent enjoyment: “… Unshakable freedom of mind, this is the goal…” [1] when achieved, then “to whatever place you go, you shall go in comfort; wherever you stand, you shall stand in comfort; wherever you sit, you shall sit in comfort; and wherever you make your bed, you shall lie down in comfort.” [2]

If you think about it, all sentient beings seek comfort, not happiness. It is only in modern times that ‘happiness’ has become our stated goal, but it is only an abstraction, not something that is attainable, and marketeers know this. That is why they are always trying to convince us that we need to buy their products to be more comfortable in some way. They know that this is our actual motivation, but they also know that desiring or craving things will not bring us happiness, nor comfort, so we will never be satisfied.

Any community that lives on staples has relatively few wants. The community that can be trained to desire new things, even before the old have been entirely… consumed, yields a market to be measured more by desires than needs. And man’s desires can be developed so that they will greatly overshadow his needs.[3]

This is the exact opposite of Buddha’s great insight about how not to suffer.

I’ll leave it at that, so you can answer your brother without getting into the complexities of how one goes about implementing what Buddha taught.

[1] “The Middle Length Sayings (Majjhima Nikaya),” Volume I, tr. I.B. Horner, Luzac and Co., Ltd., London, 1954, pg 253

[2] “The Book of the Gradual Sayings,” Volume IV, tr. E.M. Hare, Luzac and Co., Ltd., London, 1935, 1955, pg 200

[3] American Prosperity - Its Causes And Consequences, Paul M. Mazur (Lehman Brothers) 1928, pgs. 24-25