He's not chucking...he's only averaging 13.6 FGA a game (had 13 today).
He's just not hitting the shots that he used to.
Deron has always had poor shot selection for a passing/playmaker PG. (Or for any PG, really.) He takes too many 3s, too early in the shot clock. A guy like Chauncey Billups can get away with that kind of play, because he's not all that good at anything else.
He would be a better player if he got Tony Parker treatment from his coach on 3pt shooting (fined for each attempt).
And yes, he needs a coach who can actually coach. What is with all these NBA coaches who don't actually know any offense? My high school coach knew Xs and Os better than maybe half of NBA coaches.