I would beg to differ with the idea that new riders push to big and thus slow a gear. You usually see them twiddling away like nothing on earth as far as I can see. Maybe this proves that there is no value answer? Modern MTB s are geared very low and most cyclists start there and stay there. They just don't know any better and never find an efficient style.
I also find that with 2 knackered knees, with little cartlidge left, that twiddling is not good. To stay pain free I need resistance and control. I know that others stay the same.
Again. This points to any so called definitive answer being rather suspect at best. I suspect that there are too many variables. Muscle structure, fitness, weight, training and even geometry of bike all play a part. I can pedal faster more comfortablely on my TT bike with a 78 degree seat tube than I can on my laid back MTB.
My point? Just how useful or valuable is all of this?