If you cannot can save others then why is your practice more worthy than anything else?

First, the correct wording isn't "helping others": the correct wording is "helping somebody to achieve something (which means you have the faculty to help, and more importantly to discriminate between a successful result and a failure of the guy you try to help)".

Everybody knows about the "Four Brahmaviharas" (metta, karuna, mudita, upekkha); and indeed they good practices -- but if and only if the person exercising them follows the path in the first place.

For instance, if you practice "metta" without being a noble disciple, that would gets you to a good realm but then get you to a bad realm:

Paṭhamamettāsutta (AN 4.125

“Mendicants, these four people are found in the world. What four? Firstly, a person meditates spreading a heart full of love to one direction, and to the second, and to the third, and to the fourth. In the same way above, below, across, everywhere, all around, they spread a heart full of love to the whole world—abundant, expansive, limitless, free of enmity and ill will. They enjoy this and like it and find it satisfying. If they abide in that, are committed to it, and meditate on it often without losing it, when they die they’re reborn in the company of the gods of Brahmā’s Group. The lifespan of the gods of Brahma’s Group is one eon. An ordinary person stays there until the lifespan of those gods is over, then they go to hell or the animal realm or the ghost realm. But a disciple of the Buddha stays there until the lifespan of those gods is over, then they’re extinguished in that very life. This is the difference between an educated noble disciple and an uneducated ordinary person, that is, when there is a place of rebirth.

Toxic puthujjanas do not worry about the bad realm: they focus on the good realm, and even tell other people to do metta and karuna etc., without even telling them that they will become miserable.

Now on giving: it is the same situation as with metta etc. The sutta on Giving (AN 7.52) explains what is the appropriate way to give to somebody.

There are plenty of bad ways to give to somebody: giving because of tradition or lineage, giving because of "egoism", and of course giving because of "selflessness".

Some puthujjanas dislike reading this, since it goes against their faith in their fantasy that loving people and feeling good about themselves for giving stuff makes them good people!

So what is the right way to give a gift to somebody? First the right way to give a gift is to give it to a contemplative. Second point is what is the citta and mano doing while giving the stuff to the contemplative':

“Or, instead of thinking, ‘When this gift of mine is given, it makes the mind serene. Gratification & joy arise,’ he gives a gift with the thought, ‘This is an ornament for the mind, a support for the mind.’ He gives his gift—food, drink, clothing, a vehicle; a garland, perfume, & ointment; bedding, shelter, & a lamp—to a brahman or a contemplative. What do you think, Sariputta? Might a person give such a gift as this?”

“Yes, lord.”

“Having given this, not seeking his own profit, not with a mind attached [to the reward], not seeking to store up for himself, nor [with the thought], ‘I’ll enjoy this after death,’

“—nor with the thought, ‘Giving is good,’

“—nor with the thought, ‘This was given in the past, done in the past, by my father & grandfather. It would not be right for me to let this old family custom be discontinued,’

“—nor with the thought, ‘I am well-off. These are not well-off. It would not be right for me, being well-off, not to give a gift to those who are not well-off,’ nor with the thought, ‘Just as there were the great sacrifices of the sages of the past—Atthaka, Vamaka, Vamadeva, Vessamitta, Yamataggi, Angirasa, Bharadvaja, Vasettha, Kassapa, & Bhagu—in the same way this will be my distribution of gifts,’

“—nor with the thought, ‘When this gift of mine is given, it makes the mind serene. Gratification & joy arise,’

“—but with the thought, ‘This is an ornament for the mind, a support for the mind’—on the break-up of the body, after death, he reappears in the company of Brahma’s Retinue. Then, having exhausted that action, that power, that status, that sovereignty, he is a non-returner. He does not come back to this world.

“This, Sariputta, is the cause, this is the reason, why a person gives a gift of a certain sort and it does not bear great fruit or great benefit, whereas another person gives a gift of the same sort and it bears great fruit and great benefit.”

You see the situation is exactly like doing metta, karuna mudita and upekkha without being on the path first (which means at least "doing sense restraint").

Puthujjanas love to claim that it is a good conduct, because it is the actions they already do, and because the person doing them is reborn in some realm qualified as good ... before falling back to a less good realm. The most toxic puthujjanas love to cling to short term "solutions", where they will feel bliss, and they do not care that one day they will be miserable again. What matters for a toxic puthujjanas is to have the good stuff right away even though it will lead to afflictions later on.

If you have doubts on whether your practice will free anyone from saṁsāra in your lifetime

Is this an example of an aphorism "the perfect is the enemy of the good" -- which, Wikipedia says, is related to a "Nirvana fallacy" -- i.e. "if you can't be perfect, then no point trying to be good"?

what reasons can you give for why your practice should take precedence over anything else

You probably didn't mean it this way, but "precedence over anything else" may be an exaggeration -- for example it's also important (fundamental) to be harmless. An example (of your being "harmless") is keeping the four or five precepts. But perhaps this is part of your practice already.

I think it's generally a mistake to assume that dhamma is only one thing (see also here) -- to assume that you can summarise it as one thing, and ignore everything else.

I think that a generosity too is beneficial, not (or not only) for the sake of "helping others" but (perhaps more importantly for "your practice") for the sake of reducing attachment -- or practising non-attachment -- e.g. a material gift may be a small antidote to a self-view that "this is mine".

Personally I think that a great (or greatest) "gift" (that you can give) is not only dhamma (doctrine) but liberation or liberty -- or at least, help provide an environment in which someone can discover/experience (live) liberty. Perhaps you might read the Therigathas -- many of which praise mutti (in comparison to the life they had previously). Some (many) people feel they must seek seclusion, perhaps the homeless life, to be free -- which I think includes being free of evil or unwise company, free of other people's unreasonable demands and expectations, etc. IMO you might extend this gift towards monastics (by helping to support them materially) and towards laypeople (by being undemanding).

So if "your own practice" results in your own behaviour being a bit less "needy"; skilfully abandoning cravings and attachments; maybe having a better of identity (and so for example not, "he is mine" and "she is mine", and "they owe me") -- maybe that helps to answer your question.

In other words I suppose I'd answer that any of your practice is also important towards liberating others, partly because it's (only) because you practice that you're able to help free others.

Also I find it hard to blame the behaviour described in e.g. A messiah for India's abandoned sick -- that (although not explicitly Buddhist) seems to me a practice for cessation of suffering -- for example as described in the Bikkhuni sutta:

There is the case, sister, where a monk, considering it thoughtfully, takes food — not playfully, nor for intoxication, nor for putting on bulk, nor for beautification — but simply for the survival & continuance of this body, for ending its afflictions, for the support of the holy life, [thinking,] 'Thus will I destroy old feelings [of hunger] and not create new feelings [from overeating]. I will maintain myself, be blameless, & live in comfort.

Perhaps you shouldn't assume it's an "either/or" decision (i.e., 'either' your practice 'or' alleviating the suffering of others in whatever mundane way you can) -- perhaps an ideal is 'both', a middle way, a doing one by (or while) doing the other -- or one and the other at different times, like walking with the left foot and the right foot.

Also I think that a Buddhist doctrine which says that you don't give material/mundane aid, and/or that immaterial aid is superior, is intended for monks -- who (by their poverty) have a limit to the type of aid that they're able to give (e.g. they can't give money because they don't possess any) -- but who nevertheless ought to know that what they do have (i.e. Dhamma) and can give is important, worthwhile, worth offering, and superior. I think that the expectations or advice (re. generosity) for lay people is slightly different.

Generosity, kind words and helpfulness are all meaningful in Buddhism, however small. Every Buddhist and non-Buddhist should practise it. See the next 3 quotes from the suttas.

From Vaccha Sutta:

"I tell you, Vaccha, even if a person throws the rinsings of a bowl or a cup into a village pool or pond, thinking, 'May whatever animals live here feed on this,' that would be a source of merit, to say nothing of what is given to human beings. But I do say that what is given to a virtuous person is of great fruit, and not so much what is given to an unvirtuous person.

From Itivuttaka 26:

This was said by the Blessed One, said by the Arahant, so I have heard: "If beings knew, as I know, the results of giving & sharing, they would not eat without having given, nor would the stain of selfishness overcome their minds. Even if it were their last bite, their last mouthful, they would not eat without having shared, if there were someone to receive their gift. But because beings do not know, as I know, the results of giving & sharing, they eat without having given. The stain of selfishness overcomes their minds."

From Itivuttaka 75:

"And how is a person one who rains everywhere? There is the case where a person gives food, drink, clothing, vehicles, garlands, scents, ointments, beds, dwellings, & lights to all brahmans & contemplatives, to all of the miserable, the homeless, & beggars. This is how a person one who rains everywhere.

A person responsive to requests,
sympathetic to all beings,
delighting in distributing alms:
"Give to them! Give!" he says.
As a cloud — resounding, thundering — rains,
filling with water, drenching
the plateaus & gullies:
a person like this is like that.
Having rightly amassed wealth
attained through initiative,
he satisfies fully with food & drink
those fallen into the homeless state.

The next quote from Iti 100 however shows something different. It says that the gift of the Dhamma (Buddha's teachings) is superior to all other types of gifts.

From Itivuttaka 100:

"There are these two kinds of gifts: a gift of material things & a gift of the Dhamma. Of the two, this is supreme: a gift of the Dhamma.

"There are these two kinds of sharing: sharing of material things & sharing of the Dhamma. Of the two, this is supreme: sharing of the Dhamma.

"There are these two kinds of assistance: assistance with material things & assistance with the Dhamma. Of the two, this is supreme: help with the Dhamma.

"There are these two kinds of mass-donations: a mass-donation of material things & a mass-donation of the Dhamma. Of the two, this is supreme: a mass-donation of the Dhamma."

Why is this the case? Other types of gifts relieve one's sufferings temporarily. But with the Dhamma, even if one would not become free from samsara in this lifetime, it would still guide them (and us) to cleanse our mind, and at least bring us to happy destinations both in this lifetime and the next.

For according to Dhammapada 1:

"All mental phenomena have mind as their forerunner; they have mind as their chief; they are mind-made. If one speaks or acts with an evil mind, suffering follows him just as the wheel follows the hoofprint of the ox that draws the cart."

So, even if learning the Dhamma does not free one from samsara in this lifetime, at least it will guide them to be more skillful mentally. Since the mind is the forerunner to all types of sufferings (see MN 135), becoming skillful in mind, will reduce all sufferings in future.

And according to AN 3.99:

'Now, a trifling evil act done by what sort of individual is experienced in the here & now, and for the most part barely appears for a moment? There is the case where a certain individual is developed in the body, developed in virtue, developed in mind [i.e., painful feelings cannot invade the mind and stay there], developed in discernment: unrestricted, large-hearted, dwelling with the immeasurable. A trifling evil act done by this sort of individual is experienced in the here & now, and for the most part barely appears for a moment.

This shows how one could reduce his or her suffering by becoming developed in body, virtue and mind.