EJ is incredibly good at what he does. The camaraderie also feels genuine on TNT and the gimmicks work. Kenny Smith is great at communicating his points and Barkley has always been entertaining, whether intentional or unintentional.
I think TNT must have some pretty good writers helping them come up with bits to do on the show. Remember the Kenny Smith car jumping commercial attempt? That was genius. If the ESPN guys tried that, it would feel forced.
TNT managed to create something special with the right combination of talent. I don't think it can be easily duplicated. Jon Barry can be entertaining, but he doesn't have the resume of Barkley or Smith to be taken as seriously. Smith, Barkley and EJ also seem to be incredibly comfortable with one another, to the point where they can make fun of each other -- even about stuff that can hurt like legacy, a lack of championships, or weight.