I have a lot of Nikon gear, so am pretty deeply &q... (
I don't have a D5, but I do have a D850 and D500. I was in my local camera store a while ago and they had an unsold Z7 that they let me take a deep look at and take for a short spin around the block. Now please keep in mind that I was not in the market for a new camera (I'm still not), but even giving the Z7 the benefit of the doubt, it failed to make enough of an impression to make me consider buying or trading (my D810) for one.
The EVF is very popular here, but it failed to demonstrate itself to me as "better" than the optical viewfinder in my cameras. I don't shoot based on a "corrected preview," but one is already available to me on my rear display if I should need it. Construction did not provide the same confident "feel" as any of my other cameras, even going back to the D300. The user interface (menus & buttons) is very similar to that of the D850. Sometimes, just for fun, I like to shoot in square format (24x24) using the two DX lenses that I have. As far as I can tell there is no option to do that on the Z7...it changes to DX format automatically and forcibly, and I could not find a way to override that action. I did not have the camera long enough to evaluate battery life, but extrapolating from what I could observe indicated that it was going to be disappointing.
Overall, my assessment was that the Z7 would give me maybe 80% of what I already had with my D850. Since I tend to use a broad range of my cameras' functions, this was just a deal-killer for me. IBIS would be nice, but it does not serve a need that I have...the few lenses I have that need stabilization have VR, and I've never seen any evidence that I'm missing it on the other lenses, most of which are shorter lenses anyway. It also seems that Nikon is pursuing a new pricing strategy on the lenses, with equivalent S lenses being quite a bit more expensive than their F mount equivalents. The shorter flange distance means that the lenses have to be slightly longer, and the claimed extra performance from the new designs does not address a problem that I have found to be significantly real.
Don't get me wrong, though. I think the Z7 and Z6 are both very nice cameras. But their relative value depends completely on where a photographer is coming from. Either would be a great upgrade from a D7500 or even a D600. A Z7 might even be a nice change from a D750, but the cost penalty would be hard to justify. I personally would question the benefits of either camera over the D780, but can't say, because I've not used one. But I do not see a Z7 as an upgrade from a D850, and the Z6 would definitely be a step back, except maybe for video capability.
People who use their cameras differently from me could clearly come to a significantly different conclusion. I'm convinced that many here just use their cameras as boxes with sensors, shutters, and a place to stick a lens on one side. Nothing wrong with that either, but those folks will definitely come to a different conclusion from someone who routinely uses most or many of their camera's functions routinely.