Hmmm, I lack the experience flying gliders to know if I can equate my thoughts of a powered aircraft to an unpowered aircraft in this context. I do agree that a glider can perform a climbing turn without a loss of airspeed, but my very modest physics thinking about the inertia involved is incomplete when it comes to gliders.
I entirely agree that this discussion, in the context of gliders, is valid and interesting, though I'm not sure if it's the same discussion as that for powered 'planes.