Maybe that's because people don't often study things that are obvious. You quote the study's claim, but there is a context to that claim. His conclusions make a lot of sense in steady-state trainer cycling. Maybe you could show some of his graphs or data taken in hard sprints or steep hill climbs. It may not be that you add much power on the upstroke, but it may be that being clipped in allows you to add more power on the downstroke. I know in steep climb, while standing, there are very different lever dynamics going on. The only way to study that would be to measure power clipped vs platforms. To my knowledge, that has not been done.

Again, I assure you that none of the pros he worked with would race on platforms. My point is that the study you are looking at was not targeted to study what we are discussing here. It is relevant and interesting to see, but study was not examining the question of if you can produce more power with foot retention vs platforms. That study was about pedaling techniques - all using foot retention.