I think his "regression" is greatly overstated. Physically, I don't think there's anything wrong. He looks explosive to me - fast and quick. He still gets anywhere he wants to go. He's just missing more - more layups, more 10-footers, more 3-pointers. His effective FG% is down to 44% from 52% last year and he's shooting a bit less from the field and from the free throw line. So of course his scoring is a bit down.
I call that an extended shooting slump and I think he'll get over that.
My bigger concerns w/DFox are the ones that have carried over from last year: 1) his on-ball and off-ball defense are WAY too casual WAY too much of the time, often within the same game. His offseason promises about locking in defensively - and our hope that Davion's example would rub off - they haven't translated w/anything remotely approaching consistency. That's concerning.
2) As many others have noted, D'Aaron's way of "going supernova" is to dominate the ball and freelance. At his best, it's remarkable what he can do, often, playing that way. But it leaves everyone else watching for extended amounts of time and, at very least, is a waste of very good shooting talents like HB, Buddy, Tyrese, and even Richaun (in his way). IMO, this is the toughest nut to crack.