I honestly think his hitting woes are all about his bat speed, he's not a big guy by any stretch, so he can't rely on brute force to hit balls hard. With his k rate hovering nearly 10% above his career norms it would seem like he just can't get around on the ball like he used to in his heyday.
Edit: does statscast measure bat speed from hitters? If so is there a good site to analyze it?