Since he was injured last year, he hasn't even gone through a full season as an active player. For that reason alone, I would stick it out for the year. Was he rough on your son last year? If not, maybe this is his way of trying to motivate your son. Why would a head coach watch a bullpen session? Typically, as I understand it and have been told, a pitcher will interact much more with the PC than the HC. Does he love his teammates and how important is that over his relationship with the HC?
At the end of the year, if he's still miserable and the negatives outweigh the positives, then maybe you reconsider. In hindsight, perhaps your relationship/read of the HC should have been more of a factor in choosing this school?
Good luck