Expensive photoequipment "hurts". It can be hard to justify when it's just a hobby. I don't need L-lenses, but I want something better than the cheapest and slowest ones. So "prosumer" lenses is my ideal. But Canon doesn't have so many of them (neither for fullframe). I also think some of my L-lenses has been too expensive. But I closed my eyes and bought them anyway
But as you say,
if I
really wanted a fullframe kit, I could probably afford it. The thing is,
I just don't want it.
I actually had an R6 for a while. I had no hurry making the switch to mirrorless, and it wasn't until the introduction of Animal Eye AF in R5/R6 that mirrorless cameras started to look attractive to me. But the Animal Eye AF was also so attractive, that I purchased the R6 together with the 800mm/f11 to use for wildlife (I already had the EF 70-300L and some other fullframe lenses too).
I loved the R6. It is probably the "best" camera I have had. I think it feels a lot more mature than the later R7 does. But when I got the R7, I never looked back at the R6 again. Why? The R6 is a great camera, but it is not the
kind of camera I want. My lenses becomes to big and heavy for the setups I want to carry with me. And that goes both for wildlife and for the more "casual photography".
My casual walk-around APS-C kit today consist of Sigma 10-18mm/2.8, EF-S 15-85mm and EF-S 55-250mm. There's room for making it even more lightweight, especially if we get a mirrorless replacement for the 15-85mm. But it is still much more lightweight than a similar set of lenses for a fullframe camera would be. For wildlife the 1365g RF100-500L vs the 2050g RF200-800mm speaks for itself. While I can handhold the 200-800mm for a short while, I would never go anywhere with it without also bringing a monopod/tripod. The 100-500mm I pack without support most of the time.
But if we should talk a bit more about prices of photo-equipment...
Good lenses are (almost) "forever". Bodies only last a limited number of years before I feel the need to replace them. With my first DSLR (EOS 400D in 2006) I purchased the EF-S 10-22mm and EF-S 17-55mm/2.8. And when the EF-S 15-85mm was introduced in 2009 I purchased that too. If it wasn't for the change of mount, I would probably still be using all three of them today (the 17-55/2.8 as an alternative to the 15-85 for situations I want a faster lens).
The shorter flange distance of the new RF-mount does however make it possible to make more extreme or lightweight lenses. And Sigma 10-18mm/2.8 has replaced the EF-S 10-22mm, and in a week I expect the new Sigma 17-40mm/1.8 to completely replace the 17-55/2.8. And as many might guess, a mirrorless replacement for the 15-85mm would be an instant buy (either "similar" but lower weight or more "extreme" at same weight), if such a lens was to be introduced.
I don't change camera as often as I think many others do. Since 2006 I have had the 400D, 50D, 7DII and now the R7 (ignoring the R6 because it never fully replaced my APS-C kit). But for me it is still makes much more sense to use a lot of money on a lens than on a camera body. So even if I wanted that kind of camera, paying the price for a camera like the R5II would feel insane.
The subject is beaten horse. A lot of people feel provoked that I prefer APS-C, and want to convince me that I should go fullframe. And I'm probably also going to stop with this post, because the discussion will continue forever, but not change my mind. Maybe I'm in a niche group, maybe I represent a lot of other R7/APS-C shooters? I don't know... But I know what
I want.