The main rationale for the R was a smaller FF camera for travel. What really pushed me over the edge was the availability of the variND filter adapter, because two of my main lenses for architecture are the TS-E 17 and the 11-24L (I do have the WonderPana 145mm for the TS-E 17, but it’s a pain to bring along on trips, and thus I never bothered getting the even larger front filters for the 11-24). I’m still not seeing the adapter available, so I won’t have it for my trip (leaving on Sunday), but that’s ok because this trip will be landscapes not architecture, so I may take only the RF 24-105 ( I have plenty of 77mm filters).
When I want really small, e.g. for local daytime family outings, it’s hard to beat the M6.