This was my point. Shorter cranks might facilitate a more aero position, but simply changing cranks length and keeping your old position won't change much.
simply changing cranks length and keeping your old position
Keeping which position? Saddle position relative to the pedals can be set is several possible ways, so "keeping" your KOPS would mean moving the saddle back if you selected shorter crank, for example.
Ok, well if we're going to include optimisations to rider position on top of swapping the cranks then I can believe that.