I've said this before on this board, but I think it might be worth its own thread. I'm of the belief that there is a difference between a superstar and a franchise player. Obviously all franchise players are superstars, but not all superstars are franchise players.
A franchise player is a guy that no matter the team, you know that team is going to be a contender. It is a guy that you could put on the Brooklyn Nets and the Nets all of a sudden become a 30+ win team. At any given time in the league there are probably 5 or less franchise players in the league. These are the guys that consistently finish in the top 5 for MVP voting, consistently make 1st team All NBA, are 1st ballot HOFers, etc. Lebron James is your classic franchise player. Kevin Durant is also clearly a franchise player.
A superstar is a great player that produces well above your average player. You can count on this player night in and night out. You can pencil him into the all star game and an All NBA team. With the right mix of talent, this player can be the best player on a title team, but he has to have the right team to be a real contender. These guys should be in the HOF and might even win a MVP in the right season, but you aren't going to consider his team a contender year in and year out. A guy like Kyrie Irving is a superstar, but he isn't a franchise player (Carmelo Anthony and Allen Iverson seem like classic examples of a superstar that isn't a franchise player).
Sometimes the line is a bit blurry and it often takes a few years to really know the true potential of a player. For example, is James Harden, Kawhi Leonard, or Russell Westbrook a superstar or a franchise player? What about Anthony Davis or Steph Curry? It might just take a few more seasons to really determine those guys places on the echelon.
So when a guy like Mark Cuban says Russell Westbrook isn't a superstar, he might just be saying he isn't a franchise player, and he might not be wrong on that, or since it is Cuban he might just be a hater trying to drum up interest.