1) He's so good he'll play a ton. He's just too good to sit. If he's only capable at the 3 in the beginning, he can play 3 and "stretch 4" against small teams who are effectively playing a 3 at the 4. There are a lot of those in college.
2) He has to learn to play both forward positions. It's tough for skinny guys like Devin and DeAndre to develop into capable 4s, that's why it took DeAndre 2 years, but the payoff if they do is huge, for both player and team. It enables the player to play basketball, anywhere on the court, including near the basket, so even if the player is an NBA "3" he can go make plays inside when the situation calls for it. A tall player who isn't willing to bang inside ends up a liability, because the reality is that nerve conduction proceeds at a fixed velocity, so taller players react slower. A 6'8" guy is at a competitive disadvantage on the perimeter and his height only partially compensates out there. But if he can play both inside and outside, his versatility makes him undefendable: he can take smaller players inside and use his strength, height, and skills there, or take bigger players outside and then he doesn't have the quickness disadvantage. DeAndre made the investment in rounding out his game and he'll be a first round pick, maybe a lottery pick, after this year. Devin should do the same. He's taller than DeAndre and stronger coming in. He has every physical gift to become a lottery pick, and if he's not a "I don't do windows" sort of prima donna and puts in the work to diversify his game then he will be a lottery pick.
I'm sure that's what honest coaches are telling him too.
