I've seen this before, a really good athletic type tears it up in the minors on pure talent then gets hot when he goes to the show because they don't know his weaknesses yet, then the pitchers learn either what NOT to throw him or what to throw him and he struggles.
THe question now is, can he adjust or not? It's not a given that he does adjust. Some player's don't, some do. Watch his stats closely and it should become evident this season. Look for how he does against pitchers who earlier got him out. If he starts hitting them or his walk rate goes up, he's on the right track.
That's why I don't put as much value on great Minor league stats like some guys do. To me, all that means is he has talent, but in the show, talent isn't enough. The pitchers are just too good in the show to get by with talent. YOu've got to have the smarts to adjust once the pitchers know how to pitch you, that's not something a super talented guy has to do in the minors. He can just see the ball and swing there, but in the show, you've got to out think the pitchers too.