Who would have thought, the rare thread on the forum that restores faith in humanity rather than drain it. Seeing so many people speak out against invasive anti cheat systems is a welcome change of pace!
They undoubtedly could, but the performance issues are in my opinion the least important of problems that come with Anti Cheat software.
Privacy and security weigh far more heavily. And there, while Square Enix would undoubtedly do its best if they were to take such a step, even the the most well-intentioned devs' best efforts are simply not sufficient. Kernel-level anti cheat (which would be neccessary to prevent the code injection that most mods, custom launchers, fixes for XIV's awful netcode etc. are based around) will always be a security risk. Even if you trust a developer, to err is human, and when you operate on that level of system access, any error, problem, or weakness in the software can create a weakpoint that can be exploited by savvy criminals.
And attacks on uniform, widely deployed software scale incredibly well.
That makes points like this one...
...so misguided. And while some people might even have no problems with criminals gaining access to information or data about them, rights are there to protect the vulnerable, which is why it is important to defend them on principle, making the whole "nothing to hide" argument so dangerous.