This makes no sense to me. Not sure if the new owner or the GM made this call. A new coach is not going to improve this team. If Durant and to some extent Chris Paul stay healthy, they will be good. If not, no coach in the world is going to make any difference.
They traded away all their depth for Durant. They couldn't even go 7 or 8 deep in the playoffs. They need to strengthen their bench with some strategic adds and hope and pray that Durant stays healthy. To me, a new/different coach is a step backwards.
As to the Celtics, bringing in someone like Monte Williams would probably be a good thing in the long run for Mazzulla. Give him a chance to grow a little bit more before another chance at head coaching. Don't see how that happens though.