Kyle still doesn't use holds with his weighted ball program.
I get the thing that a kid or under developed player trying to develop velocity strictly by developing the arm can cause issues. Im not aware of any responsible program that advocates this.
The idea that injury prevention is going to totally prevent injury is fantasy, particularly when guys are throwing hard. The injury risk is much higher at 93 mph than at 80 mph in most cases....captain obvious I know, but, an 18 year old amateur who throws 80 mph is a vastly different animal than a 26 year old pro throwing 94.
I get what Coachcavaleaml is saying about having to work with an injured 15 year old player. But for most kids they are not going to play after high school anyway if they don't find a way to develop their ability level.
There are reasons a lot of things (training wise) don't penetrate the pro game....like others have said it is partly a culture thing and the player already possess an elite set of skills. They are not the guys who need big improvements to keep playing.