Hello David, you probably had the wrong port on your RX100VII housing. I use(d*) the RX100VI in a Nauticam housing and can use the full zoom range with the standard port. Can't comment on the G7X as I don't have one, but know 1 of my scuba friends has one and is happy with it.
In analog times I used to shoot with a setup of 2 cameras - a Minolta Dynax 8000i and standard zoom or 100mm macro in a Hugyfot housing, with a Nikonos V, 28 or 15mm lenses mounted on top of the housing, and a strong Subtronic flash with integrated pilot light. This allowed me to shoot wide and macro on the same dive, up to 72 exposures on 1 dive!
But of course this was a very heavy setup, so when I switched to digital I knew I wouldn't want another system camera setup. And I also knew that 1 flash alone isn't optimal, so my new setup includes 2 very compact Inon S2000.
The biggest disadvantage of the RX100VI/VII is the limited battery capacity. If I shoot more video, it often runs out of power before the end of the dive. But its image quality is great.
* I bought the RX100VI kit in 2018 and used only this until now, but had it upgraded to RX100VII just now.