If you bring a player in to your program under the assumption that he is going to be a shooter then for the most part you let him shoot with his own form that he is comfortable with (i.e. Denis). The only time you mess with a perimeter shooter's approach is if they have a low, Fred Brown, release point. There is a huge transition from hs, where that might work, and college, where your shot selection greatly decreases. Dom, on the other hand, is a perfect example of a situation where spending time on proper mechanics is worth it. His shot is timid and lacks confidence, but these are problems that can be fixed. He needs to stop second guessing his shot and just let it fly, that insecure hesitation kills him. He fades/leans too much on his jumpers, even if he's open, whether it be forwards or backwards, and doesn't follow through. He needs to learn to find a focal point, like the back of the rim, and watch the shot all the way through every singe time.
