But not because “you don’t get the energy back”. (As recursive suggested about a downhill bike ride which is the part i am disagreeing with.) You do get it back, but because you want to land you bleed it away to drag. And once it is bled away you don’t have it anymore.

So we don’t disagree about the practical implications for flying. I’m disagreeing with recursive’s particular statement about downhill cycling and what it implies about the physics of the problem.