I have clipless on all my bikes. I use SPD pedals with Sidi Dominator MTB shoes, which are fine to walk in for short distances. I bring trail runners with me on tour. My shoe/pedal system is extremely comfortable over a long day and enables me to do a lot of work without tiring just one part of my leg.

These studies are all silly because they do not take into account adaptation. A good example is a year long trial of Powercranks by a very experienced cyclist and racer. Powercranks require you to you pull up slightly on the backstroke, all the time. He found that they required very little adaptation and did not change his power output, efficiency, etc., because he already pulled up on the backstroke almost constantly. Going to constantly was fairly easy and didn't change anything for him.

I don't pull up on the backstroke, though I do mostly unweight the back leg. However I do pull back and push forward on the pedals, a lot, so that I can pedal using only my hamstrings or only my quads and switch back and forth. Can't do that with platforms for sure. And for sure being able to spread the workload out among more muscles comes in real handy on long rides. Adaptation is everything in repetitive motion sports and it can take years of concentrated effort to get it just right.