But I can’t help but think PvE anti cheat is more about locking people out of skins/events/dlc/things than actually being to prevent cheating. Else you could just have a button that invalidated the gains of the cheated match.

Absolutely, the original sin of computers is that the concept of scarcity is totally foreign to the way computers work and it is nauseating how much work is put into trying introduce scarcity into software and games.