I'm not sure he's unsuited tbh. To me he's just unsure on his role in the side, where he should be, when to press etc. Its all fixable but takes work on both sides. He needs good coaching and needs to apply himself well.
The bold bits are why I think he's unsuited - they are unique traits to the Premier League. The pace and physicality of the game.
It can work the other way of course, like how Macheda and Iheanacho looked like world-beaters when they first came on the scene then rapidly tailed off, but in general if a kid is doing well in one league and does nothing here, it's not a good sign that he'll improve to the point where we'd see the same sort of ability he'd have shown in the league he initially came into.