I get what you’re saying but that doesn’t justify slamming someone’s head on to the ice.
Nope, it doesn't. But it started from a nothing play at a time in the game where the Wings were clearly frustrated. It's hard to just look at what Muzzin did and say there isn't an issue with how the league handles plays like that.
The league could give the referees the ability to review the play after assessing an instigator in a situation like this. If after review they found anything wrong with Muzzin's hit they could assess an offsetting penalty to Muzzin to offset the instigator.
The instigator would still apply, but the team whose player caused the instigator would feel more justified and less slighted in that situation. They could even change the instigator so that it isn't an automatic ejection. Ejection would only be necessary in a scenario like tonight where Mantha reacted to a clean hit.
If Mantha going after Muzzin had the possibility of putting the Wings shorthanded and getting Mantha removed from the game then he probably doesn't initiate unless he's 100% sure that what Muzzin did was a dirty hit that would result in an offsetting penalty against Muzzin upon review.
Most players just wouldn't initiate in a scenario where they could get removed from the game. They do it now because it results in offsetting penalties and it kills the play by causing a whistle. If there were real repercussions then players would have to make sure they actually saw a dirty hit.