In this case, Durant's right. Cuban's definition of a superstar is someone who can just be on the floor all year nd the team automatically wins 50 games. That's why he says Dirk is a superstar.
Except that 4 of the last 5 years, Dirk wouldn't meet Cuban's superstar definition. Ever since Cuban has brought in "Larrys, Moes and Curlys" to play with Dirk, they have struggled to get 50 wins each year.