Yes I agree Michael re EF, but I think the closest to the 6D is the R. The R6 is more action oriented with it's focus and fps etc. I think someone else mentioned in another thread, that a 600mm f/11 with a R6 would be a good alternative to the 7D if you can accept the MFD and restrictions on lighting. As you're likely to have maybe a EF 100-400mm already then you get the reach when you need it, or the zoom and quality when you don't. I had the 7D, never the MK II, but I did more landscapes so I accepted the FF compromise and sold the 7D.
Now someone will do the maths and show me a 400mm on a 7D II sensor gives more pixels on subject than a R6 with a 600mm lens
, and with a 1.4x tele well there is no comparison.
But I think a R7 and the R6 would be really close in capabilities other than the sensor. Would Canon offer another action oriented APS-C sensor R that close to the release of the FF R6? I can't make up my mind.