The difference in details in more a function of the field of view, not the resolution of the camera. If you crop a 16:9 16MP camera to 4:3, the image size is 12MP. But the G5 is framed on a slightly smaller image, leading to the perception that it has better detail.
If have to get my hands on a G5 to be sure, but my wife had a G4, which has the exact same sensor/lens rig of the G5.. And in terms of absolute picture quality, both the S7 and 6P (of which I own both) are better that the G4... Bright or dark. The G4 pics were much more heavily processed, which look great on a small screen but not as good when, say, added to a printed album. I expect the G5 to be essentially the same.
Now, that wide angle lens adds value, of course. But I think that those shots will only account for a limited percentage.
I think it was a little bit of a lost opportunity that they stuck with an older main camera. Now, it'll still be a really good camera, but it could have really excelled.