I agree its dependent on the players, but other teams have injuries, other teams have players that need extra reps or classroom time. This guy couldn't get PAT and punting line play in order over the course of a half season.
So either he is ineffective at getting the lesson across or M3 is not devoting effective time to the teaching.
Shortcomings linger too long and mistakes are repeated too often for him to be doing a good job. And I don't buy a talent argument considering how the offense and defense perform.