I've found this to be true. The only lens in EF mount I still use on the R is the Tamron 85mm f/1.8 VC and only because I've spent too much on RF glass already to justify replacing it. The RF versions of the trinity fully outperform their EF equivalents on the R.It is not for people who are getting into RF, those who do that are unlikely to switch back (but if they do, they still have another option).
It is for people who are perfectly happy with EF and DSLRs.
There are still plenty of them out there and it won't make that much difference when they are going to announce it.
You have a 5D Mark III (or a 6D, etc.) and you upgrade to a 5D Mark V (or a discounted 5D Mark IV), no need to do anything else, job done.
Or you can buy an EOS R5 and get your wallet gets progressively lighter by those fancy, new and exciting RF lenses because that's probably what it will demand in the long run, not adapted lenses, which are only a stop-gap solution.