I haven’t read much about the Indo-Proto-Europeans … we could say the case might be plausible without knowing that it’s particularly probable.
Neither did I. There’s not much info in this regard. Heck, we don’t even know where they exactly came from. The most accepted theory places their Urheimat at Pontic-Caspian steppe and traces their arrival to Levant through current-day Turkey (although quite later than my “hypothesis”), another theory places them at Armenia, etc. I lean toward the Pontic-Caspian origin (IIRC it’s supported by DNA studies the most) with the slight modification that the tribes crossed the Armenian highlands (as opposed to going around the Black Sea), which nomads could manage within one or two seasons and which would leave almost no traces, and which would also line up time wise. But yes, it’s a conjecture on my part.
… polytheism … could reflect a falling away from or an exoteric misreading of profound spiritual/existential truth … we could interpret polytheism as a rationalization of the rise of large cities and kingdoms
This one is pretty clear in my book. We know of quite large cities (Jericho but especially Çatalhöyük) that date back ca. 7000 BC and the culture there was totally egalitarian. The earliest stratified societies we can find are in Arslantepe and Uruk several millennia later (in case of Arslantepe 3800–3400 BC). Also, the first “holy granaries” (aka temples) were not pompous mega-structures as we imagine them to be (standard image is that of Babylonian zikkurat, when in reality they were 1–2 store buildings of the size of a bigger family house) and the cities were run solely by priests (so no other castes except priests/shamans and then everyone else). The purpose of the “holy granaries” was to collect and redistribute food of/for the whole community.
Now, if you look at ancient animistic worldviews preserved to this day (Aboriginal and Native American) you will see that they are highly dualistic and pseudo-pantheistic, i.e. there is material world and spirit world, everything in material world is animated by spirits of essentially the same nature, but there is no hierarchy of spirits per se (if we discount that some spirits are more powerful than others). Well, and then you have a shaman — a highly respected but still equal individual who is a bridge between the two worlds. A funny side note, chief Luther Standing Bear (1868–1939) of the Lakota Nation describes the Spirit as follows (emphasis mine):
“From Wakan Tanka, the Great Spirit, there came a great unifying life force that flowed in and through all things — the flowers of the plains, blowing winds, rocks, trees, birds, animals — and was the same force that had been breathed into the first man. Thus all things were kindred, and were brought together by the same Great Mystery.”
Thus, I would say that current-day hierarchical animism (basically almost every “pagan” pantheon we know of) emerged when an idea of “absolute” was introduced into the otherwise “horizontal structure”, which allowed shamans to elevate/explain/excuse their newly acquired status (and as I said above, the god-kings/warrior aristocrats came only afterwards). But again, this is just a personal observation, kind of, “What would happen if an idea of ‘primacy’ was suddenly introduced into an otherwise homogeneous system, and it went misunderstood and/or abused?” scenario.
Would you say the conventional reconstruction of Indo-Proto-European religion as polytheistic is flawed because of the historical methods? Or is some academic conspiracy afoot?
Well, we have no clue what was the original Proto-Indo-European religion, and I would definitely rule out some academic conspiracy. What we know, however, are the countless pantheons of animistic cultures that came into contact with Proto-Indo-Europeans, and even though they differ quite a lot, they also exhibit the same kind of hierarchy.
Is the idea that nonduality was the inner, secret meaning of the pantheon, as it might have been for the Greeks (the Mystery cults versus the popular, pantheistic religion)?
Basically. But from my vantage point the only thing that non-duality adds on top of animism is the possibility of realization that material and spiritual world are one and the same, while not discarding either of them. Thus it’s not so much about the pantheon as such (which in our modern times is better handled/explained by science anyway), but the overarching unity/identity of conscious existence and phenomena. That may also explain why academia is reluctant to touch it even with a ten-foot pole and religious leaders cling to status quo.
Do you know of a book that makes your case?
Sadly, no.