Don't forget about 1dx level autofocus and tracking, but with an aps-c body with awkward handling once you add adapters, and more or less the same EVF blackout as the EOS-R while capturing at much higher frame rates for short buffer filling bursts with the M6II.
I've read all sorts of people who have had wonderful experiences using the m6ii for birding, except for the fact that you can't take it out in inclement weather and/or rough conditions, and the awkward handling because of the small size. That's why I suspect Canon is sandbagging this years first half releases - I wouldn't be surprised if the RII and maybe even the R High Rez had modes that meet or exceed the 1dxIII, with the exception of being rugged. They want to sell high end RF glass, and artificially keeping the (potentially) last 1d series ef camera better than the RF versions is not the way to do that. Next years 1d hybrid viewfinder ef/rf monster will blow this one away too.