Yeah, I also think Saki reusing the hypnosis might have unlocked a bit more than just Satoru's cantus.

The "friendly" tribe using them for their own ends is obvious and perfectly natural. That's what you would do with living gods, assuming the living gods won't kill you outright, which would also be perfectly natural. You seek from the gods what you can't do on your own. If the gods can't do it either, they become instantly useless. I think that was pulled off pretty well in this episode, especially the small moment of uncertainty when Saki made the careless comment nearing the end.