I don't think he's bad. I'd say average. Anyways - basketball isn't a bunch of one-on-one isolation plays so its not like a player can be singled out THAT often. Sure, you can be beaten off the dribble or targeted in pick-and-roll situations, but it is about team defense.
If Jordan gets beat - Ibaka will be there for weak side help defense. Same for Ibaka. I love how I draft two athletic defensive minded bigs who averaged about 6 blocks a game between them and they are being called below average/bad defenders.
Nowitzki, Lee, and Jefferson are bad defenders.
Is Jordan better than them defensively? Without hesitation I would say yes. So at worst he is below average - haha. But I think he is better than that.