Stockton, drafted at the age of 22, was a back up during his first three years in the league, playing only 18, 23 and 22 minutes per game in those seasons , while improving his efficience year after year. I don't see why Exum, who is only 21 by now, should be promoted already.
We are talking about a player, Exum, who shot 35% from the field during his rookie season - which was the second worst in the whole league among players who took at least 400 shots (
https://bkref.com/tiny/M0sjh ).
Stockton had to earn his starting job against a solid veteran and I don't see why Exum shouldn't be asked to do the same. He should play for sure, but his playing time should be the result of a balance between his ability to contribute to the team more than the players with whom he is competing for playing time and the Jazz need to develop him and teach him how to run a team - something he is far from capable of doing at this point.