Well would you consider Robben, Ribery, Costa or Coman wingers? They'll be wingers in that sense.
From what I saw at the tail end of last season, he's definitely not cracked the physical side yet. He drifted in and out of games, got really clearly tired, and was still getting barged off the ball a lot more than someone like Sterling, who is obviously physically capable despite being small.
In a years time he'll be ready, and the experience of playing in Europe and winning some silverware will be good for him.
Last season Faupala, Angelino, Tosin, Humphries, Aleix Garcia, Manu Garcia, and Iheanacho all got given debuts.
Barker is clearly better than some of those, and he was passed over. I think it's pretty clear that the management were making a point of not giving him his debut, for some reason other than his playing ability.