Mike was never a "great" shooter prior to college when he was defended by quality players who were significantly taller than him. He was savvy enough to pass the ball or attempt to drive in those circumstances. Of course in high school there were only a few quality players that had a size advantage over him.
This issue is exacerbated in college. He is short for his position. That could be offset by above average athleticism, but Mike is only average at best in that regard. He is simply neither tall nor quick. Accordingly, he has to rush his shot. In high school this was generally not a problem, but with taller, more athletic players that he faces most nights in college, it is far tougher for him to be a quality shooter at this level. He needs more time to get off his shot and that impacts his mechanics. It may be subtle, but at this level a subtle alteration of your mechanics is usually deadly.
With additional experience, there may be some modest improvement. It is highly unlikely that he will ever be a good shooter on a consistent basis in college because his lack of size and quickness cannot be overcome.
Give him credit for improving his defense and overall court awareness. The coaches and Mike have done a good job in that regard.