Theoretically, Tommy John surgery shouldn't have affected his control.
The bones should interact as before the surgery (and possibly better since the joint would "loosen up" just before the ligament let go). However, the tightening up of the ligament and the joint may have changed how the joint moves, which means that he may have to make some adjustments to take into account how his joint now functions.
Of course, it's experiences like this that make me so interested in preventing injuries in the first place. You can't always fix things once they have been broken.
I'd be glad to look at his current motion if you have any film.