Pierce may not be a star, but my guess is that if there was a small forward on a different team who was scoring 19.9 ppg and was the 12th leading score in the league and was playing fewer minutes per game (more than 3 fewer minutes than all but 2) than all but 1 of the top 11 scorers (Wade), I'd guess we'd consider him a star.
Guys ahead of him on the scoring list: Bryant, Anthony, Durant, James, Harden, Irving, Westbrook, Aldridge, Wade, Lee and Curry. I guess the 'star' label ends at Pierce.
Of course, it doesn't matter if we label Pierce, KG or Rondo stars if the C's aren't winning. Bottom line is that neither the offense or defense is good enough right now.