Sorry, but this is going to be harsh. It sounds like the kid pitches like his hair is on fire. If he continues to pitch like he does he's going to be torched in HS. High school hitters can hit mid 70's fastballs into orbit. And you can't defend a walk. So he needs to get with the program and follow the coach's advice as they are professional, experienced, and successful. Once he gains more command, better mechanics, and as he grows the additional velocity will come.
Thanks. Regarding high school hitters sending mid 70's fastballs into orbit, agree 100%! That is why he is trying to throw harder.
Regarding "once he gains more command, better mechanics, and as he grows the additional velocity will come." I do not agree with this. At least, I see no evidence for it.
Part of the reason I included the details about the pitching coach's playing career is because he had the greatest command possible. His high school career could not have been better, and it was largely due to his unbelievable command. There is essentially a 0% chance that 2019Son, or any of the pitchers on the team, will be as good in high school as the pitching coach was. But the pitching coach's impeccable command did not lead to more velocity -- at least not the velocity required to have a successful college career.