Yeah, these things can get very fraught! I honestly think the solution to situations like the one you are describing is more along the lines of people avoiding stuff that upsets them rather than sorting things into subcategories or having stricter definitions of terms though. Obviously that is harder to do in practice and a lot of the people rending their garments about other people doing fandom wrong are often very resistant to just accepting the idea that other people have different preferences to them that they find actively upsetting, but that those people had a right to those preferences. And, like, I do think there are things that it are unacceptable (e.g.

antisemitism cw

Nazi AUs where one character is an SS officer and another is Jewish

) and things that I think ought to be criticised even if they shouldn't be Forbidden (e.g. writing a canon female love interest as a harridan shrew who is trying to ruin her canonical love interest's life and exists as an obstacle to the m/m ship) but by and large I think that people kind of need to be cool with the idea that not everything is for them. And that the presence of something they don't like is not the same thing as the absence of something they do like (as in "It seems like everyone's writing X/Y, but there's nothing for my ship Y/Z and I'm bummed about that" is not the same as "People shouldn't write X/Y.")