It will take time. They knew they would need years to develop and train for the NBA game. I'm not saying that he will be an All Star next year, but I do think he will take a great step forward.
Say what you want, but he is young. Too many people are comparing him to guys that have a lot more experience. Exum has the tools, speed, agility, vision, touch. Now it's up to Snyder to help him apply it.
I get that he looks timid offensively, but seeing him excell defensively is promising. He has a smooth shot and solid mechanics. It's way too early to say he won't do anything. Give him some time to learn the Jazz System, actually play against NBA competition and grow.