Let me go up the stack one level: why does Windows allow this kind of software to install at all !? Couldn't most cheating methods be defeated by requiring a signed executable to run, coupled with a complete lock of the input methods to the signed executable running?
I'm at a loss as to why the debate here is on Valve and the devs, when I can't get past the initial step: you can install THAT on Windows?
Jeez. A walled garden gated by a bureaucratic rubber stamping process (which I'm sure can't scale with the pace of software creation) sounds awful.
Path of lesser resistance: sandbox games. And have weak (serverside)/no anticheat. Cheating in games isn't as big of a deal as malware in your kernel[0,1]. It's just not that important.
It seems to me that the security mechanisms you described already exist. But Microsoft can't prevent the installation of legitimate anti-cheat software while still letting users install whatever they want to. It is a double-edged sword, one comes with the other. Users who seek this kind of protection (i.e., OS editor telling app makers what they can or cannot do) should drop Microsoft and switch to Apple.
Also, we should not confuse anti-cheat software with malicious software: if you purchase commercial software from an editor who wants to bundle anti-cheat technology in its product, this is not a malicious installation. The security mechanisms you described are aimed at preventing the malicious deployment of code in your system, not the installation of intrusive software on behalf of the consenting user.
Yeah, just drive the final nail in the coffin of personal computing freedom. Make it so that Microsoft owns your computer instead of you. Windows clearly doesn't suck enough with its advertising and telemetry and forced rebooting, they should just turn it into iOS already. Game companies and their needs are the most important thing in the universe and it's OK to give up our freedoms and control just to play shitty online games with internet randoms.
I'm at a loss as to why the debate here is on Valve and the devs, when I can't get past the initial step: you can install THAT on Windows?