We actually have a pretty good track record with those mid first rounders that spend most of their rookie season in the D-League. Not that they became world beaters but Morris, Patterson, Canaan and D-Mo all showed huge improvements in their sophomore season and became good rotational players. Capela may already be a good back up center, and I'm pretty optimistic that we'll see an improvement from Johnson too. Dekker seems like the a player that is "NBA ready" but Ariza, Brewer, Papa, and McDaniel are all competing for minutes at that spot, I think we may see Harrell more simply out of a need for depth at the four.
If he could develop a jumper, he could be quite useful. I remember him getting blocks on Steph and John Wall his rookie season. Pretty sick defensive potential at the 1 spot.
Dekker's shot needs a lot of work and he has motor issues. The guy has elite talent but disappears for stretches. He'll need to step it up if he is going to contribute this year. Not taking plays off is something that most rookies will tell you is the biggest change from college to pro. For a guy like Dekker who struggles with that already, I expect there to be a learning curve. As an Arizona fan, I watched Nick Johnson a lot in college. I love the kid but he's just not a PG and he's never been a consistent 3 point shot. He defends and finishes well so he could see PT. But he's not well rounded enough to be more than a 7th / 8th rotation guy.