So there clearly is a part of me that feels that when it comes to real-world faith traditions it's somehow cheating if you include fantastical occurrences of the kind that really only happen in fiction.
Oh, interesting. I think this didn't bother me as much, when reading, because to me a lot of real-world faith traditions do seem to include, at least, belief in fantastical occurrences of this kind? I don't begin to know enough about the traditions you touched on in Black Water Sister to comment (although if you wanted to post on the topic some time I'd eat it up), but I feel like once you get into transubstantiation (if I'm spelling it right, oy) and saints' miracles and speaking in tongues and so on in Christianity, it's pretty fantastical, in the SFF sense. (Judaism, to the small extent I can speak for it, less so, but there is kabbalah etc.) So the leap to "the devil is real and palpable" didn't strike me as so jarring. Unless you have in mind "fantastical occurrences that don't require being a believer in the faith in question to perceive and admit to," which I can buy.

I did like how idiosyncratic it was and how defiantly it wasn't the shape you'd expect a traditionally published fantasy novel to be. So though I have all these imaginary edit notes and arguments with the MS, on some level I wouldn't really want it to be any different!
Yes, same! It's definitely in my "reread often" pile.