This.
Human muscles have a fairly narrow, peaky efficiency band.
Best human + machine efficiency keeps crank rpm in that narrow band.
Actually, the research I’ve seen shows a fairly broad power output peak from about 1/3 to 2/3 of maximum rpm. Obviously the absolute peak is about in the middle but only maybe ten percent or less down at those peripheral cadences.
That’s why those of us who ride single speed still get around pretty well even when there are some hills. I can keep it in the 50 to 100 rpm range most of the time and move along just fine.
Now, in a (non-track) race, those five to ten percent would be a big darn deal....
Otto