This is a bit of a boring debate, they played in slightly different roles, at different ages, different teammates and the makeup of the league was different. Even at ostensibly the same position, "number 10", Ozil plays more as a second striker who runs off the striker and floats out to the wings than Fabregas, who was more of a traditional advanced midfielder. Fabregas did become more like this, but at Barca.
Ozil is a very talented player but not a great one. If he's off in the summer, I'll be sad only because I know that he is unlikely to be replaced properly, not because he's been uniformly successful here
