I am a hobbyist photographer who used to engage in all sorts of photography (loved birds and bugs the most, aspired to do portraiture). Then I had kids, and now I'd say 99% of my photography is of my own family. I don't really deserve to be a part of this forum - I don't even pretend to have the artistic or technical expertise of the regulars here. I count myself fortunate to be able to afford the price of admission and then some. But I can answer OP's question: with the GFX 50S (my first GFX body) the camera struggled a bit to keep up with my kids, but it was workable. The GFX 100s, paired with native lenses, allows me to not need to think about it too much. I have an adapted Sigma 40mm f/1.4 and the combination of shallow DoF and slightly slower autofocus speed means that lens still requires a bit more thought. But if the 100s can keep up with my kids, I don't think you have anything to worry about.
However, I do have one more bit of advice. It relates to this:
Still don't agree. To the point I'd challenge you to tell the difference in a blind test.
I'm going to do my own actually. I'm going to shoot 3 images on m4/3, FF and my GFX50, print to A2, scan sections of the prints and present them here for comparison.
I did this once before. When I was brand new to the GFX system it seemed as if every shot with the 50S was gold, and suddenly my other system (Olympus µ4/3) was utter trash. For fun, I challenged myself: each day I went for a walk with my then-toddler son, choosing a different camera. At the end of the week I ingested the memory cards from both cameras, but then blinded myself. Usually I see the focal length, aperture, file name, and so on in Capture One, but I turned those off so that I was only seeing the images. Because our usual walking path was the same and my son wore the same jacket, I also couldn't easily tell where one day ended and another began.
Here's the spoiler: I could not reliably tell the difference. I would think to myself that there was some key feature that showcased how amazing the GFX system was, only to discover that it was actually my E-M1 Mk2. That happened a fair bit. It was pretty rare that I'd criticize a photo, feeling that it must have been the µ4/3 sensor, only to find that it was the 50S - but it did happen a small number of times. The placebo effect is strong with our eyes.
That's not to say that the GFX system does not have its advantages. ISO noise offered about a two-stop advantage on the GFX system (not that it mattered at the time - with my µ4/3 f/1.2 lenses, IBIS, and low-light EVF mode (slowed refresh rate to offer "night vision") Olympus remained my low-light camera over the GFX 50S). And as others have alluded to, the files are massively more malleable - although you can still blow highlights. Depth of field control, coming from µ4/3, has been a lot of fun. And of course, there's more.
For the types of shooting OP mentioned, the GFX system could probably suffice. Yet I keep my µ4/3 system and continue to buy lenses for it because the GFX system is less versatile. Some of it is in the current lens selection, and some of it is in the nature of working with a larger sensor. Telephoto shooting is an obvious example. Dumping the Sony kit in favor of going all-in with GFX could work, but it seems like you're specializing and in the process are giving up some versatility. Maybe the GFX system will gain more versatility in the future, but Sony has it now.
Personally, I think µ4/3 and GFX are a perfect pair. Aside from sharing the 4:3 aspect ratio, you can better utilize the strengths of different sensor sizes. I'm not sure you'd get the same benefit of going dual-system with a "full frame" system and GFX. OP can probably safely make the jump, but to other "full frame" users looking to dump their systems for GFX, I'm a bit nervous about making the recommendation.