The issue with Mitts defense, is that like his offense, it's inconsistent.
He can bust his tail, and have great awareness one shift/game, and then the next he'll just leave his man wide open beside the net. He can also manage the puck very well one shift/game, and then have multiple careless turnovers the next.
IMO it's not really fair to use analytics to define players you don't like, and then when it comes to players you do, say they lack context. Or that he hasn't been with the best linemates, or he's in a mental funk. The guy they traded for Mitts, who's currently just a few points behind in less games as a defenseman, didn't get those excuses, and he was basically a sophomore in terms of games played. Mitts is a vet.
Mitt's will have some good games again, but this is the player everyone should have expected they were getting when the trade was made. A good, but not great, inconsistent, 60 point tweener, that leaves you wanting more, and who they wouldn't be able to sign long term.