Then do -YOU- know why there were audio ques playing on certain people streams despite not being part of the fight? Seems pretty suspect. I will admit I don't know much about ACT myself, outside of it being a "damage meter" of sorts. But the fact it interacts with game information makes it punishable to use. While ACT itself may not have been the most "serious" of 3rd-party assistance.
The audio-ques played through a bot (which can be done. Plenty of people have done it prior with look-away mechanics as early as ARR) is certainly crossing the line, despite it being nothing more than another indicator of "Do the Mechanic." Your claim that 'People dont know until they do the fight' is ignoring the people who actively cracked into the files to find the strings.
Square Enix brought attention to this in their response. Actively calling out Dataminers. They wouldn't do that if there was no reason to.
3rd-party tools that interact with the game is a no-no. SE has shown to be "don't show, don't tell." If you don't broadcast that you're going against ToS, SE has no reason to investigate. But Streamers actively show they are violating ToS by being live. As such, people will definitely report them and SE will be required to investigate. This is how this entire thing blew up. The amount of people claiming SE is changing its rules clearly didn't read the ToS themselves.
And lastly, before anyone decides to claim they need ACT for whatever reason, you don't. You really don't. All of the defenses for it (with the exception of self-improvement) is questionable at best. SE even created this weird place that has been around since Heavensward (I think?) called Stone, Sea and Sky. Y'know. The place where you can go and practice against a target that performs some of the mechanics in the fight, while also seeing if you can reach enough personal DPS to pass.