People in the forum often talk about switchers and value for money/use cases for different systems so I would be interested to understand your thoughts on the R5/RF system and how the Z9/Z system compare and how it is good value for having both.
I'm not a full-time pro, so I don't have to rationalize my purchases (if I were and did, I would stick with one system). As primarily a hobbyist/enthusiast, I shoot primarily for enjoyment, and some cameras/lens combos do certain things better than others. Accordingly I have crossed systems to get some "best of breed" combinations.
Currently, Nikon has a tremendous lead in the long-prime category. The pf lenses are amazing weight savers without sacrificing IQ. The 500mm pf even adapted is a far lighter and more compact long lens than any other system offers. The 800mm pf is the long lens that I thought I never wanted/needed but now would never give up. 800mm f/6.3 at a fraction of the weight and size of 800mm f/5.6 lenses with the same IQ for less than 1/2 the price! The 400mm f/4.5--which we all thought was going to be a pf but is actually a more conventional design--is an amazingly compact lens as well. And the two exotics--400mm and 600mm with built-in TCs--are also unique offerings (lenses with built-in TCs have previously existed for zooms but not for primes).
Accordingly, I purchased my Z9 primarily to shoot one or more of the lenses mentioned above, and it has not disappointed. Many (most) commentators think that the Z9's AF is slightly behind Canon's (and Sony's). However, if true, it is hardly noticeable. I thought that I might switch entirely to Nikon Z, but I find that I prefer my R5 for day-to-day and non-wildlife shooting. IMO, it is more enjoyable for general use, and I prefer Canon non-exotic lenses to Nikon's.
The Canon 14-35mm L f/4 is significantly better than the Nikon 14-30mm (IQ, build quality, and range), and both the 70-200 2.8 and 100-500mm L lenses are unique in their ways (compactness and 5x rather than the common 4x zoom in the long zoom). Thus, if I picked just one system, I'd either have to give up Canon's advantage in the wide-to-long-zoom categories, or Nikon's advantage in the long-prime category. I'm not willing to give up either.