I'm coming from 40+ years of Nikon, 15+ years of Nikon digital and the past 5 years shooting M43.
I liked he M43 for its size, weight, silence, lenses. It made me stealthy and fade into the background. The files were fine at 16mp especially with good craft. Video was as easy as pushing the red button. Low light was doable but the af had issues and the files took work to make them good.
What I didn't like was that the bodies were not as robust or durable, battery life is terrible and the files sometimes a bit small except with the pixel-shifting on a tripod. Low light/high iso useable but not the best.
So, I took the plunge with a Z6, 14-30, 24-70, ftz to 70-200 which works just fine and seamlessly. It's the "tween system," midway between the M43, 7-14, 12-40, 35-100 and the FX with 14-24/17-35, 24-120, 70-200, in both size/weight.
So far, I've got about 4,000 images on it in a couple of weeks plus some video and slo-mo video. The video looks good and edits easily, the prints at 16x24 are stunning.
It's a bit larger and heavier than the M43 but not as large or heavy as the FX. Battery life is definitely better than M43. IQ a whole lot better especially higher ISO. It's as silent as the M43. Low light is a couple of stops better. Color and auto WB is as good as it gets.
So far in processing the files, it seems faster and easier to process, thus less time pixel wrangling, though it takes a little longer to download the files because they are half again as large.
I'll be using the Z6 as my primary camera coming up on a several projects in the next few of weeks and see how it does on these events I shot with the M43 successfully but I think my results should be even better and with less effort to accomplish.
So far the Z6/Z7 is the next step and Nikon has taken what it learned in five iterations with its Nikon 1, putting a bunch of that tech into the bases of the Z system. However, it's added the wide angle and prime lenses the 1 lacked. With the firmware update for AF and a few other tweaks I think it's ready for prime time.