I think it's better to stick with the Sony system, unless you hate something about the ergonomics or build quality. It's partly because you're already in it, and partly that it's a very versatile system. You can go with the R-type bodies for high resolution and have a secondary body like the standard A7 for your average shoots, or go for a sports-focused A9, and still be able to use the same lenses. The GFX system is all more specialized at this point, slower to function. There's a certain charm to it but I wouldn't want to use it as my primary camera system unless I was only shooting one or two subjects that I knew the system could cover.
It probably got lost in my big post above, but I recommend this: get the GFX again, then mix your shooting with your Sony. Either bring them both out, or use them both on different days over the course of a week. Wait a week or two before going through your photos to try and blind yourself as to which camera you used for what, and when you're going through your photos, further blind yourself by removing file labels and possibly image data, if that would reveal the camera used. Just look at the pictures, and try to guess which camera took which photo.
The reason for the exercise is that what we see and perceive is heavily influenced by beliefs. Everyone assumes a larger sensor must be better, and everyone is crowing about the GF lenses. If you believe it, you'll see it. But is the difference really there? Blind yourself to find out. As I wrote above, my other camera system is µ4/3. When I wasn't blinding myself I thought there was a huge, earth-shattering difference. When I blinded myself, I wrongly attributed photos to both camera systems a surprisingly large amount of the time. Both camera systems also tolerate going to about 200% zoom and maintaining sufficient detail. If that's the case between the GFX and µ4/3, my guess is that the difference between your Sony and the GFX will be even more difficult to distinguish if you're properly blinding yourself... unless someone wants to tell me that µ4/3 beats the pants off of Sony. (Which may be the case - I've never used the Sony system, so for all I know it's garbage and their marketing team just has everyone fooled.)
It probably got lost in my big post above, but I recommend this: get the GFX again, then mix your shooting with your Sony. Either bring them both out, or use them both on different days over the course of a week. Wait a week or two before going through your photos to try and blind yourself as to which camera you used for what, and when you're going through your photos, further blind yourself by removing file labels and possibly image data, if that would reveal the camera used. Just look at the pictures, and try to guess which camera took which photo.
The reason for the exercise is that what we see and perceive is heavily influenced by beliefs. Everyone assumes a larger sensor must be better, and everyone is crowing about the GF lenses. If you believe it, you'll see it. But is the difference really there? Blind yourself to find out. As I wrote above, my other camera system is µ4/3. When I wasn't blinding myself I thought there was a huge, earth-shattering difference. When I blinded myself, I wrongly attributed photos to both camera systems a surprisingly large amount of the time. Both camera systems also tolerate going to about 200% zoom and maintaining sufficient detail. If that's the case between the GFX and µ4/3, my guess is that the difference between your Sony and the GFX will be even more difficult to distinguish if you're properly blinding yourself... unless someone wants to tell me that µ4/3 beats the pants off of Sony. (Which may be the case - I've never used the Sony system, so for all I know it's garbage and their marketing team just has everyone fooled.)
