The thermodynamic zero-point-energy required to activate any AWES is the energy to stretch it out, plus the energy to raise its mass to altitude. AWES free-energy to do useful work is on top of zero-point energy.
At low wind velocity, zero-point need can use up all available energy, but at high wind velocities, abundant free-energy becomes available (see kitesurfing videos).
USP3987987fig5 with power kite, as originally envisioned, and as shown by this demo, is quite good compared to other AWES categories, for minimal zero-point and maximal free energy. Rigid kiteplanes are not so good as power kites for low zero-point energy, and Tallak is right that their high-velocity tether drag is more of a limiting factor.