Also dismissing the point that children create imaginary friends....does not add strength to your argument. The point is they are capable. Without anyone telling them to do it.
I do think this is being dismissed, which is a shame, because it is quite a valid point. It may be in that video too.
As to hallucinogenics---what makes more sense. They took a substance that caused them to see things, and then defined it as some parallel world and sought to experience it over and over
Or---they already had a sense of the spiritual, so when they stumbled on happy mushrooms they figured that was it.
Hallucinogenics play a pretty big role around the world to link adherents to the spriritual---so are trances, chanting, percussion---all of which can put the brain in a trancelike state. Around the world, and even here, dreams hold spiritual signigicance for many. All evidence that humans had many avenues in which the only logical explanation (pre-science) was there was an alternative reality that bled over from time to time.