Unless it happened prior to where you cued it up, Fran did not say he has perfect form. He said he has a "pure, repeatable, mechanical, simple, flawless shooting stroke, when open". The when open part is the concern for me and thats related to his shot mechanics which are far from perfect. Miller does a pronounced dip with the ball prior to going up and the release point is in front of his face instead of on top of his head to the side of his shooting hand. The dip results in a slower release and the lower release point makes his J susceptible to being affected by the defender. Perfect form is Klay Thompson's J. Yes Fran said "when it leaves his hand, it always looks like they're going in" which I again would agree with. The issue he's going to have is getting it off.
If his shot mechanics were closer to Klay's, I'd love him as a prospect. Outside shooting is largely about confidence which takes a hit if a shooter isn't sure he's going to be able to cleanly get it off. I suspect the longer quicker defenders every NBA team features will cause him trouble and question whether he's got the quickness & game to take guys off the dribble when they play too much up on him. He's got some work to do if he's going to max out his potential. At the very least he needs to get rid of the preshot dip.
STOMP
