I think it is too early to definitely call him a bust. There is a reason he was a consensus top pick (maybe not consensus #1), and was able to shoot 40+ % from 3 on 5 attempts per game for 25 games in college. Now, his FT % was concerning, no doubt, but not unredeemably awful.
I tend to believe the injury thing, but if that is the case, I do not understand the management of his injury.
Now, I am not an orthopedic doctor, but I would not be doing cortisone shots this early in the season. It doesn't really help the overall healing, it is something I would reserve for if he was needed in vital games, ie to clinch the playoffs or in playoff games, to bridge him until the offseason. Considering how many games Simmons and Embiid have missed, I would much rather have Fultz rest and do physical therapy to avoid steroid injections, especially since he seems to be learning really bad shooting habits to compensate for the pain. Why not rest him until he can shoot with preferred form? I don't get it.