I wonder if the run and gun ball weight may be a typo? My son is working with a group now (Optimum Athletes-Sacramento) returning to competition this fall (from TJ surgery). Max ball weight for run and gun is 6-7 oz. Plyos go heavier. I played catch with him the last couple weeks and noticed a shorter arm action, more consistency, and easier velocity. I didn't put a gun on him because he is not up to full effort yet,
My son studies pitching and his impression is that he is learning to reduce the peak stress points in the chain, which allows him to use more of everything else. I doubt you could describe everything going on verbally, at least not to a kid. The weighted balls are what we call a no-teach in my line of coaching; the balls do the teaching.
A very important point is the increase in shoulder injuries caused by the increased external rotation (and weak rotator cuffs). A nice thick layer of corded steel around the rotator cuff is necessary, and that takes years of training.