They've made it pretty clear that the TOS is broadly written because it makes it easier to enforce correctly.

To clarify: if you wrote a TOS that was very specific and said, for instance, "parsing tools are permitted to aid in improving job performance, but using them to be abusive will be disallowed and may lead to a ban", you would have people examining all the terminology with a metaphorical scanning electron microscope looking for loopholes, because this is the internet and someone's always going to do that -- someone's going to try to find a way to obey the letter of the law while violating the spirit of it.

And then you have people who are like, "I wasn't being abusive, I just was providing constructive criticism! Very emphatically! Like Gordon Ramsay!" or whatever, trying to argue they shouldn't be banned.

Whereas if you just say "the use of third-party programs is disallowed save where explicitly indicated, and may lead to a ban" that gives them a lot more freedom in dealing with infractions.

If someone uses ACT for personal improvement (or within their static, sharing numbers with folks on console who can't otherwise measure their own performance), the devs are likely not going to care. Even if it's on a static's stream, they're probably not going to care, as long as the numbers are just being used by that static for personal improvement.

Start calling someone out in a dungeon ("You know, the healer should just leave you on the floor. Your DPS is so bad that them just casting Glare is a better use of the MP!") and hey, look, you were clearly parsing... that's a TOS violation, so long, don't let the door hit you on the way out, goodbye.

THAT SAID, there actually are a handful of third-party tools they've said are not considered problematic in any way and which are thus actually openly okay with them: notably, ReShade and its variants, used to do depth-buffer-aware post-processing via pixel shader injection. (I.e., change the colors to be more colorblind friendly, improve shadows/lighting, turn the game into a pencil sketch or an oil painting for artistic screenshot purposes, etc.) I don't feel like looking through this forum for the thread here in the last five minutes of my lunch break, because the forum search engine is kind of awful, but there is a thread somewhere here where they do explain that.

Additionally, Nvidia Freestyle (Nvidia's variant of ReShade) lists FFXIV in the officially supported games, with Square-Enix's permission and approval; you can find that one if you hit up the Nvidia website.

(The one request they did make in those threads that I recall is that if you take screenshots using shader injection, you don't manually add in the "Copyright Square-Enix" tagline on the bottom, because they don't want shader-modified images being mistaken for stock game images.)