He's barely 20....TWENTY.
Braun was in college at twenty. So was Weeks. Fielder spent his full age 20 season in AA.
Color me unsurprised that a young hitter's weakness is offspeed low and away that breaks out of the strike zone. Chourio simply hasn't seen enough of those pitches to make that adjustment in his approach to lay off them - but he's been so good otherwise that he's having to learn to solve that flaw on the fly. It's not a swing change to fix a hole in the strike zone - it's pitch recognition and being able to spit on offspeed stuff instead of swinging at it. Sure, it's tougher to do that at the MLB level, but keep in mind Chourio is building his own mental book on how pitchers are attacking him, and the longer he's in MLB the more reliable that book becomes, too. When he starts taking those pitches more consistently and pitchers find themselves having to attack him in the zone with pitches Chourio can predict, he'll do more damage consistently.
Not worried at all...