This may be difficult but can you link it also to the stats of the player/s above them on the depth chart as i'm sure an RB would be more accepting if he had to wait behind Adrian Peterson than if he was waiting behind a lesser RB ?
Brock Osweiler just left the Broncos because he was upset that they played Peyton Manning in the Super Bowl instead of him, and got a huge contract (can I say way overpaid? Kind of felt like I was watching an MFN offseason there). I think the player who is willing to play second fiddle to a better player when he could start elsewhere is the exception and not the norm.
His expectations are based on his current ratings, not his future ratings. So a draft pick won't get as upset as he is developing, but once he's fully developed he will want to play.