How does weight enhance hip/shoulder separation & direct

How does weight boost your velocity if velocity is about hip/shoulder separation and directional momentum?

Alot of ppl in the baseball world talk about mass in the legs and adding weight, but wouldn’t you just need functional strength?

I see Mariano Rivera and say aha he is the perfect build of a pitcher. His height and weight is 6’2 185 lbs…which isn’t too much Mass.

Does it really help chan ho park to be 6’2 210? Or trevor hoffman to be 6’0 221 lbs?

But then again roy oswalt is 5’11 190lbs. He is listed at 6 foot but c’mon that is a definite exaggeration.