You couldn't be more wrong.
http://www.youtube.com/watch?v=fEQJAgIxX2A
Watch any number of the pitchers THROWING the weighted baseballs.
I have worked with many kids who have done the NPA program, and all of them throw 3 oz to 2 lb balls on TOP of the holds. Go to 9:30 in that video and see them throwing underload balls as well as doing holds.
Also read Dr. Coop DeRenne's studies on this topic that were done decades ago.
Thank you for proving my point in your own reference video. "Why do arms and shoulders get stronger? Because they hang on to the balls." "Tennis players never get shoulder injuries because they hang onto the racket. In our program, we started hanging on to various weighted balls." - Tom House.
You see the kids throwing regular baseballs in this video. They ALL hold onto the weighted balls and towels.
Now, what were you saying about being more wrong? Please stop allowing kids to throw weighted balls back and forth to each other in their warm-up lines!