Retro focus lens designs are generally used for SLR focal lengths less than 35mm. However, mirrorless designs still have a mount flange, so for ultra wides, a retro fcosu design may still be required. Canon could easily have created an ef 50mm f1.2 L that matched the RF 50mm f1.2 L optics but chose not too. The Zeiss Otus 50mm f1.4 and Sigma Art 50mm F1.4 are good examples of other brands fullfilling that particular brief. The EF 50mm f1.2 L isn't a retrofocus design, it's just one that was compromised for the need to be small, compact, bright and relatively cheap to build (Canon was going through a strange design phase at the time). It's easily the weakest L prime in the EF range.
An EF 35mm f1.4 doesn't need to have a retro focus design. So the assumption that a newer RF 35mm f1.4 would be optically superior could only point to a newer and superior design that has little to do with mount (EF vs RF). I think there would be more optical gains for an ultra wide zoom or a 24mm f1.4 on the RF mount. However, I've never found the ef 24mm f1.4 or 35mm f1.4 lacking optically. Maybe in a 50+mp world results will be different. But for wide open lenses...bokeh and rendering is king and not absolute sharpness. Stop down a few stops and most of the EF lenses are sharper than most zooms.
