2 years ago, Ingles finished third in the NBA in three point percentage. And since, by your logic, we need to discount last season (as you did with O'Neale), then you must concede that Ingles belongs in the same sentence as Conley and Bogdonavic. So that's 3 elite shooters plus two average shooters. According to this CBS Sports analysis, 38% as a team is the differentiator between a good shooting team and a bad one. When you consider the 5 players we've discussed will take the vast majority of threes for the Jazz and 3 of the 5 are good to elite, I think 38% seems quite reasonable for the team.
Yes, the CBS Sports piece is 5 years old, but the point still stands. I think what you are doing is completely discounting that the JAzz got rid of their two worst high volume shooters and replaced them with 2 high level volume shooters. They are joined by Ingles, who was already elite, and 2 average shooters. Yes, I do believe we'll see career highs in 3pt% for both O'Neale and Mitchell, because they are going to be getting much better shots than they are used to getting.