Considering the Canon R6MII

[Overread]

So I'm almost sold on moving onto a Canon R6MII, but before I commit I'm open to suggestions, thoughts, alternatives and other ideas people might suggest. Just in case there's a pitfall I've not noticed or a vastly superior option that I've overlooked.

I basically need a fullframe capable camera that's got a strong AF system and is suitable for outdoor use in all weathers for sports/action photography.
From what I can see for its price, and sticking with Canon so I can use my current EF/EFS lenses, the R6 models offer the best mix of build quality, AF features and FPS. Whilst I've some concerns over the EVF vs a mirror assembly, it seems that the much more modern mirrorless bodies (esp the mid to high range ones); have made this much less of a concern compared to much earlier models; esp when following fast moving subjects/panning and following action sequences.

Now there's still the 5D Mark IV and older copies of the 1D series of bodies in this same price range.
Mirrored cameras won't have any rolling shutter in the viewfinder at all; they will last longer battery wise and it seems like the 5DMIV and 1D series will be more rugged than the R6 series, though this last one is trickier to find solid info on. Personally as long as it can work well in the rain that's going to be my main concern.

Right now from what I can see in reviews a good many users of the 5D series are shifting to the R6 or at least happy to use both at once - though how much of this is reality and how much is people doing it for youtube videos because its the newest canon and they want to ensure they get the next newest is a hard to say. But honestly the reviews do highlight that the R6 is simply a lot newer and offering way better AF and ISO performance as well as DR and other factors. It's a newer camera and the technical side seems to really hold up well with improvements.


Other points
Getting the control ring version of the mount adaptor over the regular mount adaptor.

Getting the battery grip is a must for me. From what I can see the Canon E1 strap that I've used a lot with my 400D and 7D has been removed from sale, so I'd welcome suggestions for a suitable similar strap for the hand for use with the R6 and battery grip (or similar camera with grip if alternative is suggested).