For landscapes, the Canon is in an entirely different league, much better than, the Sony. Another great Canon lens for landscapes on the RIII and RIV is the Canon 70-300mm L. I've used them both with the Sigma MC-11.
I currently also use this lens (Canon 70-200mm F4 IS II) for landscapes.
With the MC-11 AF only works in the center part of the frame, but that's not an issue for landscapes ofcourse.
It's indeed much sharper than the Sony FE 70-200 F4. It's also much better than the old non-IS version.
Does image stabilization work on Canon lenses adapted to Sony cameras? If I were in the market for a Canon lens to adapt to my Sony camera, should I value IS over non-IS for image stabilization reasons?