I'm finding this excuse becoming weaker and weaker. As noted earlier, he is being played less than previous seasons and he is actively worse. The reality is that even as a third pair doesn't magically not come up against quality opposition. It may not seem as bad simply because there would be less opportunity for him to demonstrate how bad he is (i.e. it's limiting the damage).
I would also argue he doesn't think atm. A lot of his problems are because he gets caught puck chasing, joining the rush, pinching at the wrong times, and generally showing a complete lack of awareness. Not thinking himself into trouble.