Not to start some huge Physics debate here ... but I think there are two things at play here ... shock and vibration.
Shock is the force transferred to the racquet / player from the impact of the ball. There is WAY too much of that force for a tiny little piece of rubber or plastic that a dampener is to do anything about.
Dampeners only dampen the insignificant vibration (and subsequent sound) of the strings that result in hitting of the ball.
Well, I didn't say anything about force, but I concur with your line of thought.