Man, even "Area 51 has aliens" is a better and more backed up conspiracy theory than this. Kernel AC isn't to please MS, nor is it to shit on Linux/Steam Deck. They don't matter. They're inexistent. They're a blip of very vocal users that keep believing that Proton is going to save them from EA making shit games.

KACs exist because they want to have higher privileges to not be injected into, closed or otherwise touched by any other process. That's also why a bunch of them have started to ask for Secure Boot, so that they can guarantee at least some chain of trust that ensures you've probably not tampered with your machine.

Your Linux example 1/ turns anti cheats into not only something that analyzes what runs on your machine, but actively tries to attack it, which is the textbook definition of malware, but also a gigantic liability should you happen to say, write into word.exe because you fucked up and thought it was a cheat. 2/ turns it into an infinite game of chasing each others with you injecting into cheats, cheats injecting into you, back and forth. In addition, you're running on an actively hostile machine with a hostile user that _wants_ to fuck over your anti cheat.

Please do some proper research on the subject.

A user level anti-tampering software (and more with such linux feature) is not a kernel module which is weaponized by hackers.