You can pick out any number of other things that Udoka has done that helped the team improve, but this team was stuck because it couldn't get Smart and Tatum to change. The team wasn't going to evolve unless they either blew up the roster or those two were willing to change their offensive habits.
Stevens was wise enough to see he couldn't get to them. Uodka got it done and more importantly has now established an ethic of improvement and trust. Very, very few NBA coaches can get stars to accept a plan to modify their game for the good of the team. Usually when it happens it's because of the star, not the coach.
We now have a coach and players ethic that accepts the need to adapt. This team is going to accomplish some things over the next few years.