So if a player doesn't play well and they aren't seeing him develop they should keep him on the NHL team because he isn't developing? Let's look at your examples of under developed or misused youth. Kessel, was going to sign an offer sheet, has been on several teams, is a good player. The deal they made got them Seguin and Hamilton. Seguin was a terrible trade, if they were choosing to move on from him due to off ice issues they had to do better and did not, really the beginning of the end for Chiarelli. Hamilton is on team 3, maybe heading to team 4 and has never developed into the caliber of player expected. All of them were perceived as not being committed enough to become next level players by management and they moved on. Wheeler's trade helped them win a Stanley Cup and you make that deal every single time.
Sorry but character matters, three of your examples were sorely lacking in it here and two still are. Maybe you should question Donato's commitment to becoming the player they wanted him to become and not a one way average offensive player with a good shot.