I'm a professional musician but not on piano, and even I can tell the difference.

While it may be true that velocity is the only variable, it's not a physics problem. As a player you can't choose the instantaneous velocity for the note, and the note is played at the same time or immediately before/after other notes, which all adds more variables to the touch and the movement of the musician.

Therefore the whole action matters, including how the key travels, the decoupling point, the resistance of the multiple parts of the action, the rebound... etc

It's interesting you're happy to disregard pianists opinions on the matter. Perhaps you think experts are too mired in tradition to see the truth? That may be true sometimes, but you also don't have the same grasp of what's involved as they do.