It seems you are being selective in your comparison of the D850 to other Nikons. When I go to DxOMark, I see the following summary analysis of the camera:
Conclusion
The introduction of the first BSI sensor in a full-frame Nikon DSLR with a super-high 45.7Mp resolution puts the Nikon D850’s image quality on par with, and often better than, medium-format cameras. The first DSLR to hit 100 points — rather apt for Nikon’s hundredth anniversary year — puts the Nikon D850 in a class of its own for image quality. At base ISO, it’s unrivaled for color in the DSLR class, and its headline dynamic range score is outstanding, too. Against the competitor high-resolution options from Sony and Canon, the D850 offers either better or close to comparable image quality throughout the ISO range. Although its headline ISO score doesn’t quite achieve the same lofty heights overall, it’s still a very capable performer at high ISO sensitivities, too. So if you’re looking for the best image quality at low ISOs, at significantly less cost than a digital medium-format camera, the Nikon D850 looks like the camera you’ve been waiting for.