Your quest is not a new one. Both above and below water, photographers often want a lens that can do it all and underwater, where lens changes ares just a bit more complicated, it is even a stronger desire.
If 24-70 works for you, then try a 170 or 180 dome and see how you like it. But it isn’t really very wide, as mentioned above. Ultimately, it is very hard to get around a two or three lens setup…one for macro and one for wide angle, and perhaps a mid-range and, as you know well, the larger the format, the larger the ports, usually. If you want a non-fisheye wide angle on full frame, I think you are pretty much stuck with your big dome unless you are less demanding of corner quality or want to keep cropping extensively.
The wide angle huge dome problem can be gotten around with one of the water contact optics, but it will compromise the long end. In the end, I don't think the Z9 system is going to work the way you want.
I have never used the setup, so I am not speaking from experience, but I read here about a lot of people who seem quite happy with a Sony FF camera, 24-60 lens and a WWL that can be removed underwater, if desired. You can even add a closeup lens to the front of the flat port once the WWL is removed. That sounds to me like the closest thing to a “one lens solution” for full frame and seems like it comes closest to meeting your goals, if I correctly understand your desires and the capability of the Sony & WWL. I don’t know enough to suggest any particular camera model.
Sony experts like Phil Rudin could speak to this system better than I can.
Or, perhaps you need to consider a different format? Going to M43 or perhaps even APS-C can allow you more leeway in dome size.