I can confirm that my 50mm Summicron is not only small and lightweight, but also dead-sharp, corners included.Yes, but Leica M lenses are not that big. They are known for sharpness and aberration control. And I wouldn't say that their small lenses are not sharp across the field. And distortion? I know they have the rear element much closer to the sensor. But the RF is not that far away, as I remember.
And I'm speaking of a 1969 (!) lens, Canon, do you listen?
The newer Apo Summicron 50 is certainly sharper than any other 50mm on the market.