My bad. When you said "all", I thought you meant "all". I wouldn't want someone to think that's all that goes into development of a prospect, which is what you said. And you're correct that training doesn't matter, as long as you don't care about the pitcher's arm strength, stamina, etc. (hint: that's sarcasm). The importance of training is probably the one thing in all of HBD on which you're most likely to find a consensus.
And no, addressing his question, you are not dead on. Or do you not realize that Pitching Coaches affect development? Playing time with a Rookie League PC with a rating of 45 would not develop a superstar closer.