I agree with your premise but you can't use the RF800 with the M series. If you mean M series for cheap/small (or M + EF white lenses for reach) OR any of the R bodies + RF800mm then I concur.
Cheap reach is the reason that 7D users will claim with pixel density being the primary one. 7D users will complain that the M6ii/90D with adapted long white lenses is not useful because it doesn't have dual card/weather sealed but it does achieve the required reach parameter.
Using 7Dii + medium whites (70-200/2.8, 300/4, 400/5.6 etc) with TCs gives dual card/AF/fps with pixel density to avoid paying huge sums for big whites.
R5 price is too much for a 7Dii replacement with the 17mp crop being "vastly" insufficient cf 20mp in 7Dii and we can't use TCs with RF70-200mm/2.8 or limited range with RF100-500mm.
They yearn for the 90D/M6ii sensor but in a R mount body at a R6 price (or lower). The unanswerable question is how big is the market for Canon?
I used to have a 7D but I am happy to be corrected by the 7Dii user base for their needs