Nearly every major anti cheat implementation is ring-0 access. If you have any game with EasyAntiCheat or BattlEye installed, you've also got one. This is of course not to say they aren't a worrying thing, but they aren't abnormal and HD2 certainly isn't the only one to use it.
Kernel level Anti-Cheat has access to all the hardware and software on the computer. So if the Anti-Cheat is ever compromised through a vulnerability, then those hackers would have complete control over your system.
PSA: There is currently an RCE exploit being abused in @PlayApex. It is unsure whether it comes from the game or the actual anti-cheat (@TeddyEAC). I would advise against playing any games protected by EAC or any EA titles once they have fixed this or can comment.
Currently, the RCE is being abused to inject cheats into streamers machines, which means they have the capabilities to do whatever, like installing ransomware software locking up your entire PC.