Sounds very familiar. My 2017 is going to miss about a week of his month-long HS camp/league games this Summer due to attending a couple of academic showcases. Coach is very old school and makes similar negative comments about players not being there losing their status. What I saw last year with this Summer league was a bunch of scrimmage-type games (6 batters or 3 outs, unlimited subs, etc.) to evaluate how the Freshman and JV adapt to Varsity games. Seems to me to be less critical for the guys who already played a year of varsity, but the coach may hold it against them anyway.
We talked and my son is just going to come clean with him and explain these opportunities are his best chance to meet college coaches and gain critical exposure. He will have to work twice as hard while with the HS team and hope that the coach forgives him by the time Fall rolls around and they start practicing again. Tough to make a kid choose, but he has no choice if he hopes to play in college.