No idea what's actually going on, but my somewhat optimistic take is that as he's learning to control the strike zone, he has dialed the aggression back. Once he gets a firmer handle on when and when not to hack, he can turn it loose on hittable pitches, not virtually all pitches, as he had been. I think it's just a transition period, and I'm not worried about his power disappearing (though I think that if he ever becomes a 40+ HR guy, it'll take a few more years than we were hoping for). Do we want to see him learn to control the strike zone, or do we want to see him sock a few dingers?