The RPG mechanics didn’t ruin the genre although I did prefer the mechanics of earlier CoDs where in multiplayer everything is unlocked and you just use whatever you want.

What ruined the genre was the free-to-play style monetization and season pass paid update model.

Black Ops 2 was the first CoD to have paid skins, but we would have no idea how bad things would become. By the time Fortnite came along the multiplayer FPS genre was already long ruined