Robinson is our worst defender. This bit from MGoBlog does a good job of illustrating the gap between Wilson and Robinson on the defensive end:
This is where things get hairy. According to Synergy, Wilson was easily Michigan's best defender last year, giving up only 0.74 points per possession (83rd percentile) while taking on the most individual defense possessions of any Wolverine. Xavier Simpson (0.76 PPP, 80th percentile) was the only other rotation player to grade out above the 60th percentile, and he played a lot less than Wilson.
Robinson, meanwhile, ranked in the 23rd percentile on defense. While Oregon iso'd him to death in the Sweet Sixteen, his bigger issues came off the ball?he did a very poor job of fighting through off-ball screens and wasn't great at closeouts, two things Wilson did very well. Livers has good defensive upside, though it's hard to bank on a true freshman being a plus player in that department.