This is from The Athletic new article regarding when Fultz visited and the workout:

“The workout and physical played a role in the Celtics electing to trade the first pick in the 2017 draft to the 76ers, eventually drafting Jayson Tatum with the third pick a few weeks later. After Fultz held his initial workout with the 76ers, he told reporters, “My knee is great. As you can see, I’m jumping pretty high and everything like that. It was just a situation where I had some stuff going on with my knee.””
Looks like Ainge thought he could fix Fultz shot but seemed concerned that “something was not right with Fultz”

A few conclusions:
-the workouts are not useless. The team truly does it and not for no reason like some people try to believe
- Ainge is the best