I don't really know about Scott Alexander appart from this post. But, this one, I enjoy a lot, and I've read it like a hundred times.
I have read many of his posts for a long time, until some years ago when IMO their quality started dropping significantly. There are some other posts that you may enjoy, written around those years. I disagree with many of his points but still find them interesting and stimulating. I won't share them here because they often mention politics.
I'm really entertained by his hypothesis, but I don't really buy them, I feel they're just that, entertaining thoughts told in captivating words.
I agree with that. I've also found the book I read by him entertaining. My problem with Gallimore is that he tends to present his ideas as more than entertaining or interesting hypotheses. For example, compare how he presents his stories to how McKenna did it. Gallimore tries to pretend to be doing science while being careful enough to maintain plausible deniability about it. He often abuses formalism and abstraction, in a way that makes his text more obscure to most people without really contributing to anything more than giving it a halo of "it's abstract and dense, so it must be science".
For example, the book I read by him had a whole chapter trying to explain automata theory. If you already know automata theory (as it was my case because that's part of the field I studied) you get nothing out of it, and if you don't, you won't understand it based on that chapter. And you don't need to, it's a quite unnecessary part of his theory, which in its core is a kind of gnosticism decorated with terms from maths and science. It comes across as a trick to impress readers.
What do you mean by them failing to understand the point of psychedelics?
Well, in the case of Scott Alexander he said it himself: he doesn't see the point in them because they don't seem to give you any information or knowledge about the world, only the feeling of insight. Gallimore is similar in wanting them to be a source of information about reality, however he still seems to expect them to be so. I say "seems to" because him preferring to continue speculating ad infinitum instead of testing his hypothesis leads me to think that he doesn't actually believe it. But I may be wrong.
I'm not saying psychedelics can't possibly provide any information about the nature of reality or about aspects of reality itself, maybe they can. But to me focusing on that is completely missing the point, and honestly seems like a maneuver to avoid looking at oneself and one's own mind.
Maybe Gallimore is right, but in that case I would like to finally see data instead of more papers or books speculating, always followed by a media tour in podcasts and such hyping it up.