Little known fact: Shulgin's dick was nicknamed "Thick Slapper", on account of the sound it made while slapping his thigh as he walked.
Yeah my thought is that each psychedelics (as well as psychedelics as a whole, and also any other sort of experience, ritual, etc) connect us to a sort of read-write shared consciousness space, so not only are we affected by the previous collective experience of others, we also add our own experience to that collective. Plant medicines tend to have been used ritualistically as sacraments, ie, important, central aspects of a peoples' spirituality and view on reality. By using those plants, we are tapping into that. We are also changing that space, as well, but the history of it is still there.
One of the reasons why RCs are so fascinating to me is that they are so new. Shulgin and his friends set the stage, and then in recent times, we have all contributed heavily to the "morphological space" (I don't really like that term much as it seems sort of... not hippy-dippy, pseudoscientific, but whatever, it's a good term for it). The internet greatly increases this sharing, as we read and write trip reports, which directly influence the expectations of others.
I think the same is true of ritual, and indeed, of culture in general. We each occupy the "morphological space" of expectations, worldviews, body language, slang, and so on, of the culture(s) we are a part of it. Not only do we occupy it, but we contribute to it, in the way that a drop of water contributes to a lake. Or in the case of some charismatic and influential people, in the way a rock in a creek alters the course of the flow of that creek. That space slowly changes over time, and it changes because of the collective contributions of everyone participating. So, too, I believe, does the psychedelic space slowly change over time. I believe that a person who trips for the first time today is going to be exposed to a somewhat different space than the person who tripped in 1967 for the first time. I have no proof of this, of course, but I believe it nonetheless.