I understand that it probably frustrated coaches, and I still take issue with 'improved greatly' It is my opinion that successful coaches find a way to either improve the player (which Marlin has done on occasion) or make sure they stick to what they are good at (which I think Marlin has failed miserably in doing).
I think his teams the last few years have lacked discipline, both on the offensive and defensive ends. Part of that is knowing roles and understand where the most value is to the team. It is one of two issues, either Marlin doesn't recognize the undisciplined play (which I highly doubt) or two, he doesn't have the will/ability to enforce it with today's players. Neither is a good answer.