To me "more efficient" has a lot to do with your pedal stroke. There's the downward push followed by the upward pull. Typically on a hybrid, the pedal system is a platform pedal. On a typical road bike today, its a clipless pedal system. Thus the hybrid can only work on the downstroke.

The other thing on "efficient" is the aerodynamics, especially when going fast. Its about the bike, the frame, the wheels. Hybrid bikes may not have the aerodynamic advanage over a road bike.