It is odd how much value people seem to put on MP. The 1Dx line and previously the Dx line of Nikon have been ~20 MP range for generations. Clearly there is a significant market for that sensor size. And for those in this market, where 20 MP is enough, the 45 MP is a potential negative due to increased file size.
I actually do not see this as significantly better than the R3. Sure, there are some nice features here. But, if DPR is correct, and it is 2 seconds of shooting full RAW before the buffer fills, that is a significant win for the R3. The R3 is also lighter, it has a mechanical shutter, 30 FPS in full 14 bit RAW (Z9 dropped to a compressed RAW, according to DPR). $500 is a minimal price difference for those buying $6k bodies and mounting them on $12k lenses. Then we get into performance of AF, AF modes, etc, where I'll want to see production models compared before commenting.
Not wanting to get into a spec war, just saying, depending on how things play out, I can absolutely see where the R3 not only holds its own but may even be better than the Z9 in certain scenarios and for certain people. I think it is great for Nikon users, you have a good tool at your disposal, but my world with Canon is doing just fine as well.