You need to put more effort in 1 hour cycling session to burn the same amount of calories as in 1 hour running session. Running activates more muscles.

But cycling affects largest human muscles, which work more intensively..

I was "professional" athlete many moons ago. When we measured max heart rate, we did it on a bike first and then on a treadmill running and then bike again. My max heart rate running was +5 beats allways and I was not a single case. I just couldn't get to my max heart rate while cycling.

Depends on how you look at it. I can bike all day without getting tired, but there's no way I can jog all day. If your definition of efficiency includes duration of effort, or distance covered, then cycling is very efficient.