There's a better chance that Simmons develops into that star than the Jazz acquiring a third star through FA or trade during the next few years. Give Simmons a new environment, away from the toxicity in Philly and maybe he finds his place.
Simmons just needs to develop a floater and shoot 60 percent from the line and he will be All NBA every year.
The fit is not great, but like I said, there's a better chance of fixing the fit and development issues than there is at the Jazz getting a third star.