Exum has yet to prove he is starter material or a point guard for that matter
He proved he is a top tier defender at PG which is what this team is build on. Defense is half the game and he is great already there. He proved he improves our winning percentage on the court and our ability to win. He has proven that he can bring the ball up,he has proven he takes care of the ball, get us into plays and get the ball into the playmakers hands. He has proven that he can hit enough open 3s that defenses have to guard him. If that is all he does then he is a solid starter on our team with the roster.
He has shown the potential to be much more such as a great passer and great ability to get past his man. Assuming he stays healthy he will do all of the above plus be able to drive and do wonders in a pick and roll situation.