How much power does a helicopter need to hover a certain weight?
That's a question a good helo perf guy/gal can readily answer, I'm sure, and is one measure of the vehicle efficiency.
But hovering, while it's a very useful characteristic, should not be confused with doing work in physical terms. While it may carry an impressive payload, a hovering machine has zero velocity and is thus doing zero work - i.e. zero HP generated to the payload.
So it's a case of zero efficiency in physical terms. Whatever horsepower is used to hover the machine, there's zero horsepower output.