On a team built like the 2000's Pistons he could be the #1, but even then he would have to play a more cerebral and efficient game than he does now. Chauncey was their best scorer, but what made him great (I think he's one of the most underrated players of all time) is that he was super efficient and had no holes in his game.
Donovan has too much hero-complex to be that in his current form and his defense is just ghastly. Still, he can go nuclear with regularity and that has value. In any case, Donovan needs an elite rim protector and a couple of big, 2-way wings that can move the ball. Problem is those players fit everywhere and everyone wants them.
The Jazz emptied their clip figuring out PG and backup center and that might just be the epitaph of all of this. For all of the moaning about Quin (enough of which is valid enough that he has to go), he has not really been given the horses to play playoff chess either. Part of that is probably his fault too, though, considering his obvious power in the organization.
Where was I? Oh, right, building a team that has a water-tight 5-man lineup. Donovan or not, that's probably the template for this team/market, and they never figured that out. And yes that is past-tense.