[wim]

The R5 has great AF with animal eye tracking.

Yeah, I hear that a lot.  I can believe the animal eye tracking is good.  That's not the hard part.  There is an aspect about the AF that worries me.  This is not talked about that much, but there seems to be a tendency sometimes for the camera to focus at something beyond your subject.  And these dirty little rumors have it that with a long telephoto, you are really left in limbo.  With out a distance window you don't where you've ended up, and the shallow depth of field doesn't help.  You might find this shooting a butterfly on some foliage in a field, say.  I've heard you can try to pre-focus (which is a pain) but left on its own it will just search until the cows come home.  Particularly bad if you don't own any cows!

This was from a guy shooting an R5 with an RF 100-500.  And I had to dig for it.  He was saying the 5D was all that and a bag of chips.  Then I asked him how come he doesn't sell his 1 DX III.  You'd thing I was asking him to give away his first born!  He was, like, "No Way!  You can ALWAYS count on the AF system to get it right!"  When the R5 is good it is really good.  But when the 1DX III is bad, it is great.  Then he said the 5D AF is outstanding...when it is. 

He did love the camera!  Everyone loves the camera!  But I would like to experience the system on something less pricey.  If it's so good, put it in the hands of people who can't reach for their 1DX Mark III when the AF is taking the day off.  I think it will be fine.  But who knows?

-Mac

If near to subjects are very out of focus the AF can go to the background and stop there ........ requiring manual focus ........ I have no idea if FWs solved the issue ........... DSLRs will go back and forth until the subject is found!

That's no different with mirrorless. Even my EOS R will go back and forth, but it happens almost never, because it isn't necessary - it tends to get it right the first time. With my 5D II it happened way more often, although even then only occasionally.

I have so far only encountered this with my EF 180L Macro, in close-up-/macro -modus, with adapter obviously, but that lens is notorious for it, and to be very honest, when shooting very close with a slow-focusing lens like the 180L that is to be expected. Even so, I have never had the R stop focusing,with that lens, while I did have that happen with my 5D, 5D II and a couple of APS-C bodies.

Even with EF 100-400L with 2x extender on my EIOS R, in low light, I have not encountered any problems, BTW. With RF lenses that should even be less of a problem.

Considering the number of lenses I own and owned, I reckon this is total fake news, possibly caused by people who do not know in the slightest how to set up a mirrorless Canon camera, or people who have never used one.

That's my view, and experience.

Kind regards, Wim