[davidmanze]

How can a different camera help with the need for high ISO on an f/7.1 lens for sports photography?

That's fake news in my book.

This discussion is reaching bizarre levels - the EOS R is just 2y years old, still part of the current lineup and you folks are suggesting that I shall give up on it because the spot AF performance is poor on a single lens. And that's after repeated claims by BC that Dual-Pixel AF is the best thing ever since sliced bread. I mean seriously ...

To be frank, you are almost trolling there.

Facts:
You come across an issue (seemingly with IS movement). You also mention an issue with AF in a certain mode. I try to figure out from a distance what is going on, so I ask if you have tried with a different camera to see if the results will be different. 

Is that about high ISO and f7.1? No, THAT is fake news.
Perhaps that was not directed at my post, but it felt like you are not arguing fairly.
Anyway, f7.1 is only 1/3rd of a stop slower than f6.3, and I recall a certain "Sports" lens from Sigma...
The R6 does well with higher ISO, and one could do sports with such a lens. However, most sports shooters like to shoot with faster prime lenses.

I am not suggesting anything, other than try to figure out what is actually going on. Like, how are the results with an R6 with the same lens, doing the same thing?

It feels rather disingenuous from you when you say  "And that's after repeated claims by BC that Dual-Pixel AF is the best thing ever since sliced bread. I mean seriously ...". I am pretty sure you are not posting video samples.

 Give it a rest with more of this "trolling" s***t  BC !! ...