I see Al Horford as the best player on the Celtics.
I think they're equal. IT is a top 10 scorer and his D might be bottom 10. Horford is pretty good at offense and pretty good at defense (7/10, in my opinion).
If winning basketball games is necessary for being a superstar, then a lot of the young guys in the league (AD, KAT, etc) haven't proven it yet.
If being exceptional on both offense and defense is needed for your definition, then IT is def not one. Neither are a lot of the all stars.
If scoring points is necessary (the Carmelo Anthony approach), then he's def a superstar.