Hmmm... maybe, but not. All you have demonstrated, in the same way that
Galileo did, is the equivalence between gravitational mass and inertial mass
(physics 101), and you should note it only applies in a vacuum where the
effects of drag can be neglected, and as you rightly state it has nothing to
do with kinetic or potential energy. However, as a later post explains there
are other factors at work due to the aerodynamic effects which must apply to
any real world glider, namely the interplay between the inertial and viscous
forces due to the nature of the fluid in which we play.

Rgds,

Derrick.