Censored for all you kiddies out there:
I think his idea that the fastball is more harmful than the curveball is a bunch of poo.
Maybe it's true that the curveball might put less stress on the arm BUT
1) If you never build up the amount of stress the arm can take by throwing fastballs, it won't get stronger
2) If you never throw a fastball you'll never have a fastball. Ever heard of those coaches that abuse the deuce?
He might know how to throw a curveball and how to teach it, that part I am not debating, but throwing 'easy' pitches is taking the easy way out.