PJ3 has more potential, but he's a reluctant power forward who wishes he was a SF. He's not a SF. He tried to prove he was pre-draft, but failed miserably.
So PJ3 is a reluctant PF who hates contact. Sure he has more potential than PJ3, but the upgrade wouldn't be much, if any, in all likelihood.
Maybe that's part of why JJJ got drafted higher than PJ3, despite coming out in a weaker draft.
Same goes for Moultrie. Doesn't like contact, and would only be a slight upgrade over JJJ.
At least Melo likes contact, and knows what his role will be and accepts it.