A difference is that all the EF and EF-S lenses work 100% and better on the R camera(s) especially with the Control Adapter. All other brands changing mounts to mirror-less cannot make that claim with Nikon being the absolute worst with all AF lenses being dumped from working now. That is huge. I see the M series as its own world and applaud Canon for keeping it as it does provide a platform for development of very small light ILC system products for hikers and the like.All RF lenses, no EF lenses in 2019 sounds like a correct move for Canon. Right now, the EOS R is really only for Canon users with plenty of EF glass to adapt. No one outside of the Canon ecosystem is going to look at jumping into EOS R if they're after a mirrorless system. Getting the EOS R out last summer was certainly a good way to help prevent all the hemmoraging of customers over to Sony. But they need another two bodies (one entry level, one true professional model) and lots of glass, to bring the system around to where a new adopter would be happy without needing to go back to EF glass. Nikon is going to have the same thought process with the Z System.
And of course, low activity on EF or F mount cameras is likely to have existing customers feel, well, sort of like Sony's A-mount customers did while Sony was spending nearly all their time on E/FE-Mount stuff. It will be interesting how they negotiate the two systems, or really in Canon's case, four different EOS mounts.