I dont think he underperformed per se, the team was still just not quite there.
I mean when Luke Walton and Mike Brown took thw Warriors didnt miss a beat. You can say its Kerrs system,but he had no prior coaching experience and Steph and Klay were already bombing like crazy under Mark Jackson
Had they won a single ring under Kerr..you can say that they weren't quite there with MJ and that Kerr won with his players.
For example Gruden won a ring in Tampa Bay with a team assembled and developed under Tony Dungy.
But since Ker has taken over, they've gone to the finals every year....even before KD
I expected/predicted Kerr to fall flat on his face as a coach, because he was nondescript as a GM, and never coached before. I was wrong and he opened up that offense and the rest of the league is still trying to figure GSW out. We both remember loaded teams from the past, with great shooters that didn't win anything.