For me, the weighted baseball issue is boiled down to this: With all of the $$, research & resources available to MLB to examine the effectiveness balanced vs the risk of these programs, the vast majority have said NO to their use.
Who is the target market for these programs? Developing youth players. Developing youth players will see a spike in velocity by simply existing & aging & eating Captain Crunch cereal. Add a velo program & you can measure & see results with this group. Especially when the youth player does virtually no training.
Give me a MLB roster of pitchers who are fully developed adults who train & throw regularly as they do & add this weighted ball program & show me a spike in velocity. It won't happen. You may see a spike in injury. This is why it is not employed at the level that has the most to gain from the "effectiveness" of these programs (MLB).