Probably no need to panic yet. He's shown marked improvement on the offensive end compared to his rookie season. Remember that this is effectively his second playing season as a professional.
Even though he has clearly worked a lot on his handle and aggressiveness, I think Snyder still gives a lot of the backup PG minutes to Mack because he doesn't fully trust Exum's skills yet.
We can only hope he continues to improve and develop under Utah's coaching staff. I actually think the AIS/CoE bear some responsibility for these current struggles. The fact is Exum came into the league with a very low offensive skills base. His handle was (and to a large extent still is) very loose, he had limited to no dribble moves, his shot was slow and mechanical, and overall struggled to create his own shot against a set defense. The AIS/CoE has arguably never had a guard prospect with a better physical profile and star potential than Exum, but they didn't maximise that potential with proper skills development.