One last thought that may or may not play into the conversation, only because an assumptive correlation (probably more like two) has been made but not actually tested...and that's that a softball contact with a bat is or would be the same as that of the tested baseball to bat collision...and that the "vibrations excited" within metal alloy bats are the same (or similar) as to those of the tested wood bats. I'll just leave it at that.
I would definitely be interested in learning more about the differences between baseball-wood bat vs. softball-composite bat. No only in regards to how the difference in materials affects the equation, but also the difference in masses.