Dissymmetry lift is not 0 lift at retreating side and plus with multi blades also gets the benefit of multi wings instead of a pair. And rotorcraft limits 150kt Vne not only preventing shock wave but also to make sure retreating blade still plane air faster than relative air flow.
Never said it was 0 on the retreating side, just that the limit to the aircraft's lift generation is the retreating blade.
Be nice to have an advancing blade on each side, and not have to worry much about the retreater.