Buddhism is not like Christianity, where the source of truth is a book or a canon, and that the book must be believed in order to subscribe to the belief system. Speaking of Zen, at least, it's one of the foundational tenets that it's "a separate transmission, outside the scriptures." In fact, there's a lot written about how Zen isn't a religion at all, at least not in the Western sense, with beliefs, faith, and doctrines. You don't need to believe anything to be a Zen Buddhist. So even if the "Buddhist cannon" has "batshit insane stuff," who cares? Shakyamuni was a great teacher, but that doesn't mean that he can't be wrong.

> I think it's more honest to say that you practice meditation with Buddhist characteristics than to say that you're a real Buddhist if you don't have the time of day for spirits and deities

You might be under the impression that Buddhism is somehow theistic or dualistic. But the Buddha, for one, outright rejects mind/body dualism, which therefore rejects the possibility of spirits and deities. Some traditions, like Tibetan Buddhism, have tantric practices like deity yoga, which involve visualizing deity-like figures, but even then, there's no presumption that these deities actually exist, in some kind of spirit realm. But even if there were Buddhists who believe in "spirits and dieties," again, who cares? It's not like you have to believe anything to study and practice Buddhism.

My main point is that, if you're writing about meditation, or meditative practices, that either originated with Buddhism or were developed through Buddhism, it's fairly disingenuous to completely divorce it from its context.