That's a weird hill to die on, but it is, of course, your choice.
This is absolutely not remotely true with a root kit which could mess with all sorts of things, especially if you have multiple installed. And it won't be clear what is causing it.
It's not a weird view at all, it's perfectly pragmatic.
I understand that propietary things like the graphics drivers are inevitable to install on Windows, but what Riot does with their Vanguard anti-cheat system is crossing a line. If you look up the documentation on how to disable it, this piece of software loads every time your computer boots, and to enable it again the computer has to be restarted, so the kernel module can be loaded again. Most games will load any anti-cheat mechanisms when opening the game and run it only while playing. After you exit out of the game, every single process related to it is killed. This is different from having Vanguard constantly running in the background, with maximum privileges regardless of what you're doing.
The most benign explanation would be the misguided attempt by their system architects to solve the cheat problem by abusing client resources because it was easier.
The malign explanations border on conspiracy theories, but benign or malign, I too refuse to allow it. Cheating is a scourge of multiplayer games, but this isn't an acceptable solution.
Isn't all anti-cheat systems exactly that? Is there a way to differentiate any proprieatary driver to what you describe?
I can understand these measures being taken in game consoles, but most people use their PCs for a lot of stuff, and most likely store sensitive information that they wouldn't want to risk being exposed to some potencial malicious entity.