Am I getting too good at SP videogames or is it just the mouse aim?

I'm not bragging here, it's a point of discussion, I feel like so many games where aim plays any role give you a smorgasboard of tools and tactics and it all pales to "be somewhat decent at mouse aim". Is it because they're heavily designed around controllers? Is it just wasted potential like so much else? Am I too dumb to do sick nasty useful combo on the AI or am I simply god's chosen gamer?

EDIT: I play on normal, usually. I know, there's my problem, but it's not like the underlying problem gets solved via requiring 3 head shots or having to interact with a half baked stealth system that either doesn't work or mostly works on "sit invisibly in a bush until the patrol walks their 30th circle on this route"