Only slight overuse issues... He led the school in innings, pitches, strikouts last year and was pitcher of the year. I'm not OVERLY concerned. he's not a pitcher as much as he is a hitter and he's pretty good at telling the coach when he's sore... they listen.
I'd classify the coach as a grumpy old guy.... so what. He can deal with that.
I think it's more about the fact that it's not fun to lose and the way it's happening. He puts a lot on himself. He feels that he needs to be perfect and if he's perfect they have a chance to complete. Being good, the coach relies heavily on him to be perfect.... I do think the weight of the team is on his shoulders. I think this tension makes playing not fun.
I would say that learning to deal with that pressure is a good thing... embrace it.
Again, I know what you're thinking and going through. Not easy to be on losing or average high school team and good enough to be on a 16U Perfect Game WWBA Championship team.....that was my son a few years ago. He hated losing but it gave him new opportunites to stand out, separate himself from others, and be a leader on his high school team. My son is not much of a talker. He led by example, and it got the respect of his teammates, opponents and other coaches in his District. A couple of those coaches commented to me after games that my son had a "knack and a gift" both as a pitcher and a hitter.
High school coaches talk and it didn't take long for college coaches to show up and some area scouts to take notice. Playing high school baseball is just another opportunity for your son to showcase his skills, leadership, and demonstrate he is ready for the next level. I think if he treats it that way, he will relax and not feel as though he has to carry the team. Trust me, I've been there.