I think what happened is that he was not happy to be traded to Dallas and even less happy about being traded to Washington. Now he is happy. He was always a good player, albeit with durability issues. Even though I don't think he was bought in at DAL or WAS, he always played hard and actually continued to put up pretty good numbers all along. Career about 20 pts, 8 rebs, 36% from 3, 2 blocks, 2 assists, and more than serviceable defense/rim protection.
Keeping him on the court is a fair concern of course. He has had injuries, and will likely have them in the future. But I think we can work around that.
He and Doncic should have dominated. It was major failure by DAL. DAL sent out Porzingis and a 2nd to WAS for guard Spencer Dinwiddie and forward Davis Bertans. Ouch.