Being a mom myself, I know we tend to be too protective at times.
Couple of things, stop asking your son what's going on, he's gonna play on your emotions, he has to go back and speak to the coach himself, what am I doing wrong coach, what's the problem. Speak up (not in a defiant way when spoken to), the more he lets the coach know he can manipulate him with his tone, the more he might. Do this FIRST. Perhaps as an older player he needs to be a leader, that may be why the coach is ragging on him. Sounds like the team has no leadership.
Also understand that sometimes the better players get their heads banged in because of higher expectations.
Stop with the how good he is (using D1 signee as an example) and how bad the team is. That has no revelance and above all remember this is HS baseball, it will be over soon.