A deflationary explanation would be a naturalistic one that explains something away, like an eliminativist explanation of consciousness. The biologists would be explaining away gods and spirits as social instincts or some other illusions rather than crediting the supernatural with an independent reality.
The problem with basing the supernatural on entheogens and on psychedelic experience is Occam’s razor. What’s more likely, that the ancients communicated with extraterrestrial beings through altered states of consciousness or that they were naively treating their hallucinations as real?
And by “naively,” I mean that they would have done so without any information about how the brain works or how the Earth isn’t central to the universe or how our species evolved from the other animals. They would have been childlike in that respect, just as even today children naively speak to their invisible friends, treating them as real, trusting instinctively in fairytales made up by adults (such as the story of Santa Claus).
There can be truth in fiction too. A fiction can be metaphorically or existentially true, but not literally so.
I’ll have a look at part 2.