I don't see a lot of fault from Devers. He wanted to play 3B and secured that promise as a condition of signing his contract. Everyone knew that he sucked at 3B, nothing has changed since then.
They supplant him with Bregman and he's upset because he was lied to and stabbed in the back. I really think it's understandable at this point.
He meets with the team and instead of demanding a trade, he takes one for the team and moves to a DH role. He plays really well in that role. Devers looks good at this point, if anything.
Then Casas goes down and they ask him to switch to an entirely new position once again, one he has never played before. I understand the view of some who criticize him for not wanting to move again, but consider the context. He's been lied to and betrayed, but takes the high road and performs well. Then when they try to do it again, he stands up for himself and gets publically shamed by the organization. I can certainly picture myself being upset, were I put in the same situation. Can't you?