energy expended and work are not the same thing
one can take a lever and pull on a load till they collapse from exhaustion -but if the load does not move - no work has been done.
The electric motor and the watt meter experiment -tho simple - showed the relationship of thrust and watts (energy)

An inefficient prop did notchange load appreciably.However, rpm changed all over the place
a drag brake -instead of the prop would have produced a different result -obviously -