Weight suspended from the neck is really valuable weight to get rid of - going from 2085 grams (D850 with 24-70 VR) to 1135 grams (Z7 with 24-70) around your neck is huge. Yes, you lose a stop, and if Nikon made a high-quality 24-70 f4 VR in F-mount, about half the weight savings would go away (about half of it is that the f2.8 lens is big and heavy, and the Z-mount version will probably be only modestly lighter).
There is presently no 24-70 f4 compatible with a camera with a high-resolution, high-DR sensor other than the Z-mount lens and the inferior Sony "Zeiss". Canon makes one, but their sensors aren't as capable as the Sony/Nikon group. Nikon makes a variable aperture 24-85 (not in the same league as far as I know), and a 24-120 f4, and Sony makes a pretty good 24-105 f4 (as does Canon). The lenses with much longer telephoto ends are quite a bit heavier, although the range is useful, and many initial tests suggest they aren't close to as sharp as the Z lens (most testing shows the Z as very, very sharp in the central 80-90% of the image).