I absolutely would use a "trusted gaming mode," even if that meant a separate partition just for those few games that need it.

I'm not familiar enough with the technical aspects of how kernels and bootloaders handle the various launch procedures to ensure they haven't or aren't being tampered with, but I think your idea sounds like a good compromise between, "It's my Linux to modify," and, "It's my Linux to use." There's not exactly a ton of games that require anti-cheat, so I think giving up a little freedom for those few games (which you would be anyway, due to anti-cheat) with a separate mode/system is justifiable.