I got such accustomed to the Df, since 2014, that any response may be biased by my own inertia. It is not about hostility to change or aversion against EVFs - I have started using Olympus cameras some years ago and found them a delight; it's just that m43 sensors imply a bit more "chemistry" and the results are not as rich as a full-frame RAW file.
Access to ISO and, above all, exposure compensation is much easier on Z6/7; to me, the latter is a big plus. I was never enchanted by the handling of exposure compensation on Df.
Manual focus is, I'd say, a draw - Z7 can achieve critical focus with more ease than the Df (zooming in the EVF is better than zooming on the rear screen in live view mode), but under less critical circumstances, the Df seems a bit easier to focus.
I have the impression that, for a Df owner, there is no compelling reason to switch to Z6/7, except you'd badly need the extra pixels or the extra dynamic range. Another reason could be, the 50/1.8 Z and its intrinsic qualities - that lens has no real F-mount equivalent.