That's because he isn't - plain and simple. He's a good role player.....he does have the right attitude. Cauley-Stein can learn. Just too much for a B-level player.. Now it could be he comes out proves us wrong - I hope he does.
Is he worth that price tag? Considering role and production potential of course not. The same would go for Nikola Vucevic or Horford if signed for even more even if they are capable of living up to it somewhere else. It depends on what the proof you intend to see is. Is it individually based on his production? Is it based on the teams success? In the role he had last year you saw how he fits and it makes the team better, or it should if used right. Players like Nic Batum, Otto Porter, Galinari, Barnes, and so on get paid what they do because of the necessity of having that type of physical ability at that specific position. And in todays NBA you can't survive without a combo F. Hence, they will be paid a premium.