Mitch should be playing around 10 minutes a game, preferably with another skilled big in the lineup. Instead, he's playing almost 15 mpg, often as the lone big in the lineup.
There's a concept called overexposure. Its basically when a solid, but limited player is asked to take on a role that exceeds their skill level, often by necessity. We saw this the last couple of years with Landen Lucas. It caused quite a discussion on this board on more than one occasion. The truth is that Landen was never a bad player, just that Landen should never have been the primary big man. Forcing a guy that should be a secondary option into a primary role does nothing but expose their flaws in ways that other teams can exploit. That was not Landen's fault the last couple of years, and it is not Mitch's fault now.
Mitch has done a good job of trying to stick to the things he is good at, and avoid trying to do things he simply cannot do. However, in 15 mpg, the action will find you because Mitch is probably playing 5 or 6 minutes per game more than he should. That's 15 more possessions where he can be targeted on either offense or defense.
When I was in high school, my team, like a lot of schools, lacked size. We just didn't have many true big guys. As a result, we had to kind of mix and match to keep up with teams with some size. That often meant that either I or one of our other guards ended up matched up on the other team's power forward (I'm 6-0 tall and more naturally suited to play either PG or SG). On the perimeter, I was a top notch defensive player, as I could handle the quickest PGs or switch off and play the best wings. I often guarded the opponents best perimeter player. However, when I had to guard the other team's PF in some of our lineups, I was overexposed. I could usually hide out there for three or four possessions, but after that, I was probably going to get destroyed - not because I was a bad defensive player, or a bad player overall, but because I just couldn't handle giving up 4+ inches and 40+ pounds in the post. It was a mismatch, and everyone in the gym could see it.
Mitch is in the same position. He can get by okay for a few possessions at a time as the primary big, but after that, he probably gets exploited because his limitations are exposed. If he were playing as a PF, where he has done well at times this year, he can be effective, or in lineups where he is the primary big against teams that can't hammer him with size, where he has also had success.
But if you're leaning on him come Friday to handle Mo Bamba on his own for 7 or 8 possessions in a row, that's not really fair to Mitch because that's a bad matchup for him.