Pitchers are typically the worst batters on the team simply because they stopped practicing it at some point between high school and the big leagues. Most, if not all, were probably great hitters in high school, and perhaps college, but as they made their way through the minor leagues, coaches pushed them to focus solely on pitching.
At this level, they’re doing hyper specific workouts and recovery intended to keep their throwing arms strong and healthy. There simply isn’t a good way for pitchers to also fit in the type of batting practice and strength training needed to become great hitters as well, which is why it’s so rare to find pitchers that can also hit as well as every day batters.
And despite these extremely focused training regimens, Tommy John surgery is becoming more and more common, mainly because pitchers are throwing harder than they ever have. The elbow wasn’t designed to sustain amount of force over and over, and all pitchers that throw that hard are at risk for these tears. The good news is that a lot of pitchers actually come back stronger from this particularly surgery. The bad news is that it takes an entire year or more of rehab.
We’ll definitely see Ohtani pitch again, but not until 2020.