Meh.
Probably because I was reading a lot of "he should be banned from the league and arrested" tweets when I saw this last night, I'm fairly meh on the whole thing. I mean, yeah you should not hit someone in the head with their helmet and he should be suspended for it. But otherwise... The helmet to helmet hits against defenseless players bother me more.
The dude picked Rudolph up BY THE FACE MASK LIKE A RAGDOLL, ripped his helmet off and then hit him over the head WITH HIS OWN HELMET. That is a far cry from the defenseless player situation. Neither is good but this is 100x worse IMO. I get how the defenseless hits happen - you could easily assume that the player is more aware of his surroundings than he is. This situation is a pure rage moment.
Your description is a bit one-sided.
This was a fight. Garrett tackled Rudolph aggressively after the ball was long gone. Rudolph didn't like it and tussled with him, grabbing Garrett's helmet and trying to rip it off. Garrett retaliated by pulling off Rudolph's helmet. Rudolph tried to get Garrett off him by kicking/pushing him in the nuts. Garrett backed away while being pushed by the offensive lineman. Rudolph came after him yelling and continuing the fight. Garrett swung at him with the helmet around the guys holding him back.
The fact that this was a "pure rage moment" is why I'm not as annoyed by it. That's what happens in fights. People get enraged. Rudolph was also clearly enraged. The problem here is that Garrett didn't have the presence of mind in that moment of rage to not hit the dude over the head with the helmet. Clearly bad and deserving of punishment. But, like, I think Burfict's behavior over the years was way worse.