In my (probably overly simplistic view), a generator-motor system will have roughly constant energy efficiency as you make it larger and larger, while the energ

In my (probably overly simplistic view), a generator-motor system will have roughly constant energy efficiency as you make it larger and larger, while the energy efficiency of a purely mechanical system will decrease, as you spend more and more energy on moving the mechanical connections which increases in mass by the cube, while your energy gathering surface goes up by the square. So for example if you had some wind drive automata that plowed a field for you (and assuming constant wind), if you were talking about a machine that worked 1m^2 per minute, a purely mechanical system would have higher energy efficiency. But if you made the design larger so it could work 4m^2 or something, the now you have higher energy efficiency with a generator-motor system.