Just a guess.
you're saying if you took those same eight gamera rotor blades and arranged them in a pair of quad bladed rotors in a stacked coaxial orientation you'd generate significantly less lift?
your glib answer didn't help me understand your point.
The coaxial unit you posted has half
the rotor blades Gamera has. 4 blades rather than 8 blades. So they would have to rotate much faster to create the same amount of lift. Then there's the fact that the upper rotor creates most of the lift as the lower rotor is running in the prop wash of the upper rotor. The purpose of the lower rotor is to overcome the effects of torque, and since torque isn't much of a factor in human powered craft, this design is not really practical.
Now think about the amount of energy a human can create and the amount of drag the drive system would create. (It would take a lot of gearing to get the rotor speed needed. More gearing = more weight = more energy needed to attain flight.) After overcoming the drag of the drive system, there wouldn't be enough energy left to create lift. That's basically the crux of the problem these engineers are trying to overcome.