The Digital Picture has posted the image quality of the 600mm f/11 on the R5. It's only one copy of the lens and the usual caveats but the 100-400mm II + 1.4xTCIII at 560mm on the 5DSR seems distinctly sharper with better contrast, especially at the edges where you would expect a prime to win.
It's due to the lenses not just the difference between the sensors as he has compared the same lens (200mm f/2L IS) on both cameras, and they are very similar.
Canon RF 600mm F11 IS STM Lens Image Quality
View the image quality delivered by the Canon RF 600mm F11 IS STM Lens using ISO 12233 Resolution Chart lab test results. Compare the image quality of this lens with other lenses.
www.the-digital-picture.com
It's due to the lenses not just the difference between the sensors as he has compared the same lens (200mm f/2L IS) on both cameras, and they are very similar.
Canon EF 200mm f/2L IS USM Lens Image Quality
View the image quality delivered by the Canon EF 200mm f/2L IS USM Lens using ISO 12233 Resolution Chart lab test results. Compare the image quality of this lens with other lenses.
www.the-digital-picture.com