1) 1DX Mark II was a professional grade with 1 CFast and 11 CF Express Type B slot.This is a professional grade camera, even the 1dxmiii was dual CF express. A sports action camera 30 fps where one card writes slower than the other? Make sense to you? If you can afford a 6k body you can afford another CF express card, they are much cheaper these days.
2) R3 is considered by Canon to be a prosumer camera like the R5 is.