Sure, I agree with all of that. But regardless of how we can explain it away, or how the story/game might do it... At this moment, for Autumn and Hazel, it's a profound religious experience that gives them proof of their beliefs. Even if they're being manipulated by that belief.
If I'm not mistaking, the religion predates the discovery of the Elves. That said, I do think that these entities are worrying about their own safety right now, which is their motivation for genociding the Elves.
Another real world example, some native Americans used hallucinogenics in their rituals. They certainly had experiences thanks to those rituals (actually, this is true in the cases of many religions, but that is another story). It might also be part of why their religions have so much in common.
Yeah, the religion did exist before coming to the new land, but that doesn't mean that it wasn't changed then, or that the 'fairies' or whatever didn't use that against them. The elves' religion had to be even older, since they are, but still, they could have used that against them, or maybe they were already doing something like that with the elves, when they humans got there, and just added to it.
'Fairies', turning invisible, spies on the religious leaders, learn their myths, and use them against them. Simple. Hell, there could have even been some of the 'cherubs' were the fairies of the 'old world' who secretly traveled with the missionaries as part of their work.
There are a lot of ways it could be, but we need more info. to know for sure. XD
If my idea about this being a group of 'fairies' or something similar, using the religion to manipulate people, is accurate, it could also be that this has been going on forever, and this is one of the secrets that the high elf queen is hiding, by controlling her group of fairies, but the ones manipulating the humans were able to stay hidden, thanks to humans not living as long.
IDK, there are so many ways this could be happening.