Pretty much agree up until the last sentence.
I think the Jazz role for the 4 is to work outside in: has to be able to hit a 3 before being able to make use of other skills. Niang was a versatile, all-over-the-court threat in college, but until he solidified the 3-ball and proved he was a threat there first, he didn't fully fit the Jazz's scheme. In the Jazz's system, I don't think Brantley's 3-ball is ready to unlock his versatility yet.