Justified? No. But if I take a cheap shot at a player late in a game which has essentially been decided, I'm going to keep my head on a swivel, and not expect to get "dapped" up following the game by the guy I just cheap shotted a few minutes earlier. But nobody has accused Smith Shuster of having any self-awareness.
I'm not aware of Mahomes punching anyone (maybe in part because he knows he might get punched back?) while in the NFL. He comes off as a petulant whiner - its; easy to be graceful in victory, and the Chiefs have won a lot since he's been in the league.