I said I hate the 'person is actually a trans/queer/etc' because I don't think those things should be twists, I think they should just exist in the narrative and not be a Revelation(tm).

Yeah, I agree. Unless it needs to be a twist, but if it does, it has to be done with care. I read a book where a character realized she was gay or bi (she wasn't sure and it was never really confirmed), and she thought back to a creepy lesbian she'd dealt with and was all, "but I guess not all lesbians are creepy." REALLY? The book could've dealt with that so differently.