Again...I think Young's turnover rate is down mainly because his role is much smaller. In college he was scoring nearly as much as Oklahoma's other starters combined. In the NBA, his scoring rate is down significantly...behind not only Doncic, but also fellow rookies like JJJ, Ayton, Bagley, and Sexton who were inferior pure scorers at the college level.
And to be clear, I realize that Young and Morant's turnover rates are not completely out of proportion with their usage rates, so I wouldn't red flag them based on that alone. But put those turnovers in context for Morant, e.g. 10 turnovers against Eastern Kentucky in his last game, and that's not something you can easily sweep under the rug. Young has a solid excuse in that he faced a top-5 strength of schedule in college...Morant has no such excuse for his sloppiness.
All that said, I'd still consider Morant at #3 because of that rare combination of athleticism, shooting potential and point guard potential, and the fact that there aren't any players other than Zion and RJ who look like typical high-lottery picks. But he's one of a dozen imperfect options.