Took a walk today and brought both my Z6 with 24-70 f4 S and my D3s with 50mm 1.8G.
My thoughts:
The older camera is nicer to shoot with. It's just more organic, for want of a better description.
The folding screen and live view on the Z6 makes low or high level shots easier.
The Z6 is faster in many ways, but not at starting up and it gets started up a lot as I turn it off often to preserve the battery.
The Z6 files I felt needed more post production work with the D3s files being nicer.
I invariably ended up at about 50mm, give or take, on the zoom lens.
The grip on the Z6 is better.
The vertical grip on the D3s is lovely to have and makes portrait oriented pictures much more pleasant to take.
Having physical buttons instead of either menus or button press+ dial turn is much nicer.
The EVF usually looked washed out and I preferred the OVF.
The 24-70 on a 24MP sensor is very sharp, but that doesn't make it a better lens or the photos it takes any better.
The battery life of the D3s is sooo much better that I don't ever have to consider taking a second or third battery like I do with the Z6. Or powering it off between subjects.
I'm not going to get rid of either but its nice to know that for many different types of photography affordable kit from nearly 18 years ago is still in the fight today.