Not unexpected. A lot of teams don't throw to the side of the field that he's shading to. That's why you see him coming in late sometimes on those deeper passes. He's shading to the other side and has to make up ground. Believe me, McCourty (along with Hightower) is the least of our problems on defense. The team needs a consistent pass rusher, a DT that can push the pocket and/or demand consistent double teams, and improvement from the CB2 and nickel corner positions. You take away McCourty and this unit may be aong the worst defenses in the entire league.
Now, that being said, a case may be able to be made for swapping him and Logan Ryan. Move McCourty down to CB across from Butler and play Ryan at safety. I have no use for Ryan as a CB but, should he be able to keep his head toward the quarterback, he should be able to make some plays on the ball. The Patriots will lose the range that McCourty provided back there as Ryan doesn't have the same speed, but one could still make a case for it nevertheless.