I was interested in the R and 50mm together, but no longer since I saw the The Digital Picture images. For the cost, I hoped for sharpness exceeding the other 50mm lenses and matching the Sigma 135 Art. I'm sure the AF is fine, but that's not enough.
Here are some statements from Bryan, of The Digital Picture:
"Ready to be impressed? Check out this comparison (visualize the resolution difference) "
Canon RF 50mm f/1.2L compared to the Canon EF 50mm f/1.2L Lens
"This might be the 50mm lens you've been waiting for."
"The R with the RF 50 f/1.2 easily rules over the 5D IV with the EF 50 f/1.2."
Bryan does outline in detail, that the default sharpness of the EOS R is different to the 5DIV. He also explains to take these differences into account.
The combination of the EOS R and 50mm sets a great benchmark for a FF with AF 50mm f/1.2 lens.
Having said that, if someone can't get great to amazing images with a EOS 5DIV and EF 50mm f/1.2 - then it's probably the photographer!
Photographers with decent skill get amazing photos with the EF 50mm f/1.8 STM and EF 50mm f/1.4- with 'lesser DSLRs'. As I have said for 20 years in digital photography, it is often more about the skill than the kit.