Jesus you need how elastic works explaining to you?
Why do you think catapults are made with elastic and not string...?
If you drop a pebble off a bridge and then shoot one out of a catapult which one will hit the ground first?
Joe, no one was arguing about the force of an object returning down (or elastic potential energy). Releasing tension on both, there will be NO tension on the muscles involved. Zero....None....Nada.
Die on this hill if you want...your thinking is flawed.
However, using your pebble and then catapult.....
Height of 10 DB being dropped = 4ft. that would result in approximately 40 ft·lbf (≈ 54 J)
If you let go of a 5lb resistance band, the force is less than 10 ft-lbf
Now, you want to talk velocity of the object. This is NOT what the whole discussion is about. Of course the band will have more velocity as there is recoil involved with the band whereas the DB has none. Then again, if you use a 5lb band and a weight of 10lb db, the DB actually (potentially) may hit first if all you are doing is letting go of the band and not 'launching' it into the ground.
The force of the dumbell will be constant due to no change in weight and the effect of gravity (i.e. g=9.8 m/s sq.). As stated above, the band has elastic potential.