Those two cameras are really quite different.
The answer you're looking for is the 12-50mm Olympus M43 lens. It has a macro option on the lens that with Nauticam's gears and port you can access underwater.
I believe there was an underwater setting discussed elsewhere in the forum but I have a feeling the firmware updates stopped this?
I was massively into the G11 (Which I had for a long time and served me very well) and then I started frothing on the G1X mk2... but the thing is, in my opinion, they're just not that good for UW use.
Plus, having to stick to one subject underwater might help hone your skills