I turned off the continuous auto focus as soon as I got my R, so, if there are any issues that haven't been addressed by the two firmware updates I am not aware of them. I have yet to figure out why anyone would even want continuous auto focus. Eats up the battery and puts more wear and tear on the lens.
As far as the single card slot, despite claims by many, that's really more of an issue for a pro such as yourself then most users of the camera. Wouldn't make a difference to the OP I would think since so far as I know the 6DII only has a single slot.
For the sports I occasionally shoot, basketball as well as F1 and Indycar, I stopped using my 7DII when I got the 5DIV. I liked the results better despite the lower frame rate. I expect I will like the results with the R even better even though it has a slightly slower frame rate then the 5DIV.
Did I misunderstand? You stated you don't have an R or RP but you are buying R mount lenses. You can only mount them on an R or RP. I assume I read that wrong and would appreciate a clarification.

What are your reservations about the EOS R? Actually, the EOS RP is closer to the 6DII then the EOS R. Essentially the same sensor at a very reasonable price, although, the 6DII is currently priced the same as the EOS RP. Until the sale ends, anyway. I love my 5DIV and hated the idea of the market moving towards mirrorless. Until Canon came out with their full frame EOS R that is. I took the plunge a few months ago and bought the EOS R and the RF 24-105 f/4 L. I have barely touched the 5DIV since then. In fact, I've thought about selling it rather then letting it just sit on the shelf and collect dust. I have yet to find anything of consequence that the 5DIV can do that the EOS R can't do as well or often better. I really think you would find the comparison between the 6DII and the EOS RP to be about the same. The auto focus is the big thing for me. It is spot on virtually every time. The 5DIV does a good job in auto focus but the R is near perfect. I recently bought a 2x extender to use with my 100-400 L II. That combo on the 5DIV would leave me with no auto focus. On the R I have full auto focus capability. The new RF lenses for the R and RP seem to be exceptional, based on my experience with the RF 24-105, plus, with the included adapter I can use any EF lens as well as EF-s lenses if I had any. All of my EF lenses work as well or better on the R.
So, you might want to take a closer look at the RP or the R , if you have the budget. I very much doubt that you would be disappointed in either.

It depends on the application and the subject. I sometimes record video of a process and extract a still for a training manual. But if the subject is moving, quickly, I have two challenges.

First, SMOOTH video relies on a relatively slow shutter speed of 1/48, 1/50, 1/60... for 24, 25, or 30 fps. The blur “fills in” the time between frames. But stopping fast action for a still photo requires a fast shutter speed. If I use that much faster speed required to stop action, the video will look fluttery or jerky!

In those situations, I’m glad I have a hybrid camera that records decent stills and video, separately.

How would you like 227,000? Seller faked (Photoshopped?) a display of 227 in his ad. Claimed it had been a gift from his Mom that he'd never used because he had another Canon he was accustomed to and satisfied with. So this one sat in a closet because he didn't want to hurt her feelings by getting rid of it. I was skeptical, but the camera, other than a scuffed view screen, is absolutely pristine externally, and CRIS found no issues other than high shutter count.

As you say, keep on clicking! Although, my clicking doesn't bring in the bacon around here.

A new reply to your prescient input is a good way for me to try to report back to all those who were kind enough to chime in when I asked for input on this topic that, at the time, had my head spinning. I choose yours because ....well, you'll see.

I now have a Canon 5D Mark III that looks virtually new. The book's cover lies. Shutter count is beyond predicted lifespan. Significantly. I did get it at a good price, but was also misled about the camera's usage. Still, I won't worry about that issue until it the shutter quits clicking. (Anyone know what Canon charges to install a new shutter? Everything else about this camera says it'll be worth it, but what will reality say?)

With the 5D, I still have the Lumix GX85. Yep, you were right! With that 100-300mm lens on, I'm getting fine wildlife closeups. I've put my 45-150 f/4.0-5.6 lens up for sale, since my other two lenses cover the span from 12mm to 100mm.

My third camera is now a Rebel T6s, which happened along before this thread essentially died with me saying I was biding my time with what I had for the time being. (Short time being.) That model was brought to my attention as a good, lower price-point APS-C Canon also by someone else in this conversation.

I've just this week added to my L lenses with a used Canon 24-105mm 1:4 L IS USM Macro, and I've put the last 2 of my EF-S lenses up for sale (another suggestion made here that resonated). Also very recently purchased a used Tamron 28–300mm F/3.5-6.3 Di VC PZD AF for those times when I want compact, light-weight versatility. For now, the lens usually residing on the T6s is a Tamron SP AF 28–75mm F/2.8 XR Di LD Aspherical [IF] MACRO, but with the 24-105L available, I might just decide to sell this nice little lens. It just works so well, I'd hate to part with it.

Anyway, while I intend to add just a few more short, specific notes, this is my THANK YOU to all who took time to comment here.