Hmm lots of food for thought there, thanks.
So the "shock absorber" theory seems to me to have merit. My concern with it is, or was, that car "shock absorbers" are actually dampers, and without them a car would bounce around all over the place. It's the springs which soak up the initial push from a bump in the ground and the dampers allow the suspension travel to reset, but slowed down so that the car doesn't straight bounce back up and lose traction. I can't see any damping going on in the buttons I have.
Two thoughts occur in response to this train of thought:
1. Perhaps all the damping that's needed is in the mass of the plunger itself and the small frictional losses of sliding in the tube.
2. Or, after watching the slow-mo vids many times, I'm wondering if in fact the system does not need to be damped as such, and the bounce back is a good thing, to kick the arrow shaft clear of the riser and reduce contact?
From the vids it does seem that the button contact is a very short period in the initial part of the power stroke.