Who are his instructions coming from? If they are the coach, then throw the fastball and if he gets lit up then he gets lit up. If they are from someone else, then the coach needs to get involved. I would also say if he is a true pro prospect then he better show he has several secondary pitches.
I'm not gonna get into this again deeply, but I'm not a fan of catchers calling the game. They don't do it in major college baseball so why would a high school coach let them. I've watched this year and in 20 plus games I've only seen what I thought was 2 college catchers calling the game. The coach was calling the rest for both teams because i know our coach calls the pitches for every pitch.