What's the difference between having Crosby as my 4th line center and Vasilevskiy as my backup? Might as well throw the 'unhappy' player scheme out the window. As a GM I'll tell the player that I was able to fit their cap onto the team, so they should just shut up and play wherever they're told to play.
The whole reason a player would say they're unhappy is because they're being buried in a position that doesn't befit their performance. Hence, a starter shouldn't be a backup. The whole 'happiness' meter, is to maintain parity as well.