Hey man I'm trying to not come across as pedantic but did you check and listen to the first link in Scientific American where they state that Prof Tobin's work is the result of in depth number crunching? It's not speculative.
The physics and physiological research can be summed up as 10% muscle mass increase leads to up to 5% increase in bat speed which correlates to a 4% inrease in exit velocity.
An excerpt:
Tobin initially argues that a 10 percent increase inmuscle mass leads to the batter supplying a 10 percentgreater force to the bat, resulting in a 5 percent increasein bat speed. The argument is essentially oneof energy conservation, where the work done by thebatter in applying a force to the bat over a fixed distanceis converted to kinetic energy of the bat. Since kinetic energy is proportional to the square of the velocity,a 10 percent greater force leads to a 5 percenti ncrease in bat speed. In a “Note added in proof,”Tobin revises his estimate downward to 3.8 percent,based on Robert K. Adair’s argument that the workprovided by the muscles is converted to kinetic energythat is shared between the bat and some fractionof the body mass of the batter, mainly the arms.2 Theessential point is that both the bat and the batter’sarms are moving. Therefore not all of the work providedby the body muscles goes into kinetic energy inthe bat, and a fraction must also go into kinetic energyof the body. In an unpublished article that I haveposted on my website,3 I have estimated that onlyabout half the kinetic energy goes into the bat. Withthe additional assumption that half of the batter’s presteroidweight is muscle, Tobin and I both agree that a10 percent increase in muscle mass can lead to abouta 3.8 percent increase in bat speed.