Interesting discussion concerning energy transfer. I wonder if the size of the lever has an impact. Or more the size in relationship to the process.
I would say, "YES," size of the lever AND WHERE THAT LEVER IS IN THE CHAIN.
I think most people would agree that the elbow does add speed to the pitch....
Would anyone disagree that the joint that connects the lower arm to the upper arm (the elbow) makes the whipping action of the lower arm (a relatively long lever) possible. And, given that relatively long lever is near the end of the chain, that lever probably adds more to speed than any other lever. The K drill and how fast you can throw by just using it comes to mind.
Comparatively the wrist and fingers range of individual movement is much smaller in the process. So maybe any speed that is added is on the degree of tenths of mph instead of something measurable.
I agree that comparatively the wrists and fingers range of movement is much smaller, BUT they are at the end of the chain, thus they don't have to be as large/long to add speed, not in terms of only a few tenths of MPH, but more than that.
As I see it, wrist and finger flexion is vital in generating maximum speed in the internal rotation release. I think good wrist and finger speed due to great wrist and finger flexion through the release phase is vastly under-appreciated. The wrist and finger action is applied through the largest arc of motion in the overall pitching motion. And you don't think this wrist and finger action adds much to speed????