Well, leaving aside the problem of taking off (which today is improving thanks to electric motors), I guess one could say that gliders[1] are the closest we can have to human-powered flight and it's highly efficient in terms of energy consumption

[1] https://en.wikipedia.org/wiki/Glider_(sailplane)

It's "not very good" not because people are this or that, but because... it isn't very good yet: which means it needs to get better.

That's exactly what inventing is about: making (existing) things better, until they're so much better, they become a different thing altogether.