Was Buddhism during the life of the Buddha unique in the history of religion per Huston Smith?

Having read the question, what I can say is that Buddha Dharma is not a religion. It is a living system. I can also say that Buddha Dharma can be practiced by anyone but to understand the teaching of Buddha you have to be an intellect.

The following quote comes from the chapter on Supernormal Elements from the book "The Authenticity of the Early Buddhist Texts" by Bhikkhu Sujato and Bhikkhu Brahmali.

From their analysis, we find that:

• The supernormal elements only form a very small part of the Pali Canon
• The supernormal elements are only peripheral to the main message and does not affect the core message of the Buddha's teachings
• The supernormal elements are very obviously an addition by later editors of the Pali Canon
• The supernormal elements that were later additions are easily identifiable and distinguishable
• The supernormal elements did not make the Pali Canon an unreliable transmission
• The supernormal elements were added because they were part of the worldview of the society in and after the time of the Buddha
• The supernormal elements were added also because they added prestige to the Pali Canon

EBT = Early Buddhist Texts

Apart from the significant evidence from the Dīgha and Majjhima Nikāyas, an analysis of one of the main sections of the Canon that deals with supernormal beings, the Sagāthā Vagga of the Saṁyutta Nikāya, shows that they are almost exclusively confined to circumstantial material found in the narrative sections. The Sagāthā Vagga contains over 200 Suttas in which the Buddha is seen in conversation with divine beings. However, in only 21 of these does the actual conversation, as opposed to the surrounding material, suggest that one of the parties is non-human. Further, 15 of these 21 are conversations with Māra. But since Māra in the EBTs is often a name for a psychological state,it is likely that this is so in the majority (perhaps all) of these cases too. This leaves us with only six Suttas out of more than 200. But even this number does not give a fair representation of the state of affairs. All of these six Suttas consist of no more than the exchange of a few inspirational verses. They either lack doctrinal content completely or it is very limited. That is, we are probably not dealing with the sort of core doctrinal material that might be considered untouchable.

The notion that discussions between the Buddha and supernormal beings are rare or absent is also implied by a passage in the MahāparinibbānaSutta (DN 16.2.17). The Buddha is approached by the brightly dressed and flamboyant Licchavi princes, and, apparently amused, he says to the monks that for those who have never seen the gods of the Tāvatiṁsa realm, now is their chance, since they look just like these Licchavis! If the gods were visiting the Buddha regularly, filling the entire monastery with radiance,as the stock passage describes it, the monks could hardly have avoided noticing this.

This quick survey does not cover all the Suttas in the Pali Canon in which the Buddha is seen conversing with supernormal beings, but it probably comprises the vast majority of them. What we find, then, is that supernormal beings are no more than peripheral and mostly mentioned either in stories or in the narrative material that surrounds the core doctrinal content. In other words, whatever enhancement the EBTs underwent at the hands of redactors was limited to the circumstantial material and did not affect the core message of the Buddha’s teaching.

We do not mean to deny that the EBTs express a world-view in which supernormal phenomena are a part. Indeed, it is likely that this very world-view was partly responsible for the inclusion of such material in the narrative sections. That, and the prestige that this may have given the Suttas in the eyes of the intended audience, is sufficient to explain why it is there. There is no good reason for thinking that the existence of these elements shows that the transmission of the core doctrinal content has been unreliable.

Regardless of the actual status of supernormal beings, powers, or events in the life of the Buddha, the argument by Collins is of a peculiar sort.He moves from saying that later generations “could have” invented the Buddha’s statements—a straw man argument, since no-one disputes something so obviously true — to the general assertion that we have “no way”to distinguish transmission from invention. As we have shown through-out this essay, there are in fact many ways of distinguishing invention from transmission. Moreover, these are little different from the kinds of ordinary distinctions that we make in all forms of discourse. For example,consider the frequent evocations of “God” by American politicians. Do we assume that, if we are professionally agnostic towards the existence of a creator deity, we have no grounds for knowing whether any statements by that politician are true? Of course not. We take their religious beliefs as religious beliefs, and do not expect to find hard evidence for them. And we evaluate their factual claims by reference to knowable facts, just as we would do for anyone else.

To remedy this apparent discontinuity, I think it is wise to look at how the Buddha taught and what methods we proposed to attaining peace. If he were to propose a viewpoint that focused on the pragmatic path and not the esoteric, that would leave one to believe that there is no points at odds. That is not to say that there is not a Buddhist phenomenology or ontology, but that the Buddha did not propose the investigation as a proper means of attainment.

Regarding the Sutta mentioned by Andrew Skilton:

Kappam va tittheyya kappavasesam va. Comy. takes kappa not as "world-period" or "aeon," but as ayu-kappa, "life span," and explains avasesa (usually "remainder") by "in excess."

Comy.: "He may stay alive completing the life span pertaining to men at the given time. (Sub. Comy.: the maximum life span.) Kappavasesa: 'in excess' (atireka), i.e., more or less above the hundred years said to be the normally highest life expectation."

Among the numerous meanings of the word kappa, there is, in fact, that of time in general (kala) and not only the duration of an aeon; but the meaning "life span" seems to have been ascribed to it only in this passage. Also, the meaning "in excess" for avasesa (usually "remainder") is unusual.

The four constituents of psychic power (iddhipada) are concentration due to zeal, energy, purity of mind, and investigation.

• Access to Insight note on Mahāparinibbāna Sutta

Now, let us look at how the Buddha taught and the overall focus of the teachings.

In the Alagaddūpama Sutta (MN 22) the Buddha discusses views and will help in the search for your answer. It is much too long to summarize in the post, but it provides an underpinnings of the pragmatic aspects

The Dīghanakha Sutta is another sutta we can look at to see how the Buddha viewed esoteric fixed views:

“There are these three kinds of feeling: a pleasant feeling, a painful feeling, and neither-pleasant-nor-painful feeling. On the occasion when one feels a pleasant feeling, one does not feel either a painful feeling or a neither-pleasant-nor-painful feeling. One feels only a pleasant feeling on that occasion. On the occasion when one feels a painful feeling, one does not feel either a pleasant feeling or a neither-pleasant-nor-painful feeling. One feels only a painful feeling on that occasion. On the occasion when one feels a neither-pleasant-nor-painful feeling, one does not feel either a pleasant feeling or a painful feeling. One feels only a neither-pleasant-nor-painful feeling on that occasion.

“A pleasant feeling is inconstant, fabricated, dependently co-arisen, subject to ending, subject to vanishing, fading, ceasing. A painful feeling is also inconstant, fabricated, dependently co-arisen, subject to ending, subject to vanishing, fading, ceasing. A neither-pleasant-nor-painful feeling is also inconstant, fabricated, dependently co-arisen, subject to ending, subject to vanishing, fading, ceasing.

Here we see that the Buddha, focused on what we perceive rather than views about what we perceive. Earlier in the sutta, he discusses some Brahmans view with respect to please: All is pleasing to me, All is not pleasing to me, and 'A part of me is pleasing; a part of me is not pleasing'. The focus here is not a categorical answer of what is and is not pleasure, but how we relate to the pleasure and the nature of the pleasure.

“Kassapa, the statement, ‘With the one who acts being the same as the one who experiences, existing from the beginning, pleasure & pain are self-made’: This circles around eternalism [see Appendix Two]. And the statement, ‘With the one who acts being one thing, and the one who experiences being another, existing as the one struck by the feeling’: This circles around annihilationism. Avoiding these two extremes, the Tathāgata teaches the Dhamma via the middle: From ignorance as a requisite condition come fabrications…. From birth as a requisite condition, then aging-&-death, sorrow, lamentation, pain, distress, & despair come into play. Such is the origination of this entire mass of stress & suffering.

• Acela Sutta

The point I'm trying to make is that the Buddha was very thoughtful in how and why he answered questions. He focused on what led to the end of suffering, which was not focusing on the esoteric teachings (in most cases). We see time and time again that he speaks in terms of suffering and the cessation of suffering. Thus I conclude, that there is no disconnect between the two.

This is not a direct answer persay, but I hope this can spur further discussion

References:

Skill in Question: How the Buddha Taught by Thanissaro Bhikku

Buddhist Romanticism by Thanissaro Bhikku

Skilton is deeming as valid to the very accoutrements Smith & Novac have suggested are invalid. On the subject of Skilton's opinion, the monk Bhikkhu Sujato provides his own opinion, as follows:

DN 30 Lakkhaṇa (“The Marks of a Great Man”): The early texts refer several times to a mysterious set of bodily characteristics known as the “marks of a great man”. These are said to fulfill a brahmanical prophecy that one who possesses such marks will either become a universal emperor or a fully awakened Buddha. Normally when the suttas present something as a brahmanical teaching, it is in fact found in brahmanical texts. But in this case no trace of such a doctrine has been found, so the origins of this mythological idea are obscure. The story of the two paths is a classic mythological theme, found in the oldest known myth, the story of Gilgamesh. The marks of a great man exist as a curious counterpoint to the rational teachings found in most of the suttas. In this particular sutta, the Buddha is said to have explained each mark as a consequence of a specific kind of kammic deed. The literary and verse styles betray this as a late composition, and it has no real parallel in other collections. Nevertheless, it remains as a testament to the evolution of the idea of the Buddha, relating his spiritual qualities to his physical presence.

The Long Discourses: Dhamma as literature and compilation

In short, the Dhamma refuge is defined as follows therefore anything outside of this definition cannot be deemed as True Dhamma:

Svākkhāto bhagavatā dhammo sandiṭṭhiko akāliko ehipassiko opaneyyiko paccattaṃ veditabbo viññūhīti

The Dhamma is well expounded by the Blessed One, directly visible, immediate, inviting one to come and see, applicable, to be personally experienced by the wise.

Since Buddhism contains the Tripiṭaka, which officially or undisputedly includes many later compositions, such as Abhidhamma Pitaka, parts of the Vinaya Piṭaka (with new doctrines) and parts of the Khuddaka Nikāya; it is plainly clear there was a Buddhist clergy with the institutional power to add teachings into what became the Tripiṭaka. In other words, the power to add to the Sutta Pitaka and to attribute such additions to the Buddha himself.