In my opinion, those quotations are broad-brush catchalls that tend to treat this populations in a bundle.
Pitchers are an individual that must be trained, coached, managed on a one-on-one basis.
On the other hand I can understand the application of such, even some of reasoning. In other words I can understand "some" limits due to the limited number of pitching coaches skilled enough to train, coach and manage the amateur ranks.
However to be honest about the numbers given - specifically, I can't argue against or support them one way or the other. I just don't know enough about the youth game.