I think it is likely that Canon is not trying to just duplicate their EF lenses with RF lenses. In some cases, yes, we have the same lens in both formats, but I truly do believe Canon's philosophy (at least for now) is what they stated when they introduced the "R" - that the new mirrorless line will co-exist with their existing
DSLRs and EF lenses - not replace them. I know forum dwellers have a hard time accepting that
DSLRs and EF lenses will still be made, but I think only time will tell if more people prefer the EVF or want to stick with the OVF.
Thus, if the two lines (EF and RF) of lenses will co-exist, it would be stupid of Canon to just duplicate all the EF lenses. Anyone who has spent many $1,000s on an L telephoto, is likely to just keep that lens and use an adapter if they buy an R series camera. It makes far more sense - if you are making new lenses, to widen the variety, and create lenses for a wider base of consumer. So, if they already have L lenses that are expensive, large and heavy, why not make some RF lenses that are cheaper, lighter and smaller? If that's not what you are looking for, you still the choice of buying what you want in the EF lineup.