ACT is starting to become the standard 3rd party app it feels like, the devs are going with turning a blind eye on it.
Idk what the number of users but in XI we had Windower and nobody ever got banned to my knowledge from using it and it was probably used by large marjority of its PC playerbase in its glorydays.

Now the small dev team that maintains XI has implemented the core features (that most people wanted) into the XI client so of course they could add a in-game parser if they chose too, difference is they are "too scared" people being picked on which is a lame excuse imho.