Hahaha... definitely a new use of an acronym
So, sounds like there might be some issues going on with the C so tough for us to advise without being in tune to the situation. Maybe it's something more important than fastballs and curves. Maybe son can appeal to him that way... "hey, everything OK? I can't get better as a P and you can't get better as a C if all we're doing is throwing FB's. What's up?"
If still no response, at some point, maybe son has to go to the HC but, at the same time, lets him know there might be something deeper going on with C - express concern. Since son is one of two top P's, he likely has some leverage to be able to bring it up.
Meanwhile, make the best of it. There is plenty to be gained by becoming really effective via well placed FB's.