Efficiency can also be seen in different ways.

The GCN guys are testing efficiency in terms of maximum wattage output in a controlled setting for a short period of time. As I said before, for long distance touring the efficiencies could be not needing to think about where the foot is on the pedal, always having the foot oriented in the best position, being able to "float" the foot etc...

And as I said, those efficiencies may diminish if the conditions change such as if you start and stop a lot, don't do high mileage or ride rough terrain.

Here's a pic of my buddy after he just fell while clipped in. We are bushwhacking a section of the Trans Canada Trail between road sections and he chose his clipless gravel bike while I used my platform off road bike. This section required more effort from him because we were on and off the bikes a lot.






Here's a pic where I am doing long days on hwys. Here clipless was more efficient because I dismounted infrequently, and then often only one foot down for pictures..