Update. So, I've been using the A7iii quite a bit. No traveling, but family candids over the holidays and a local museum. I have to say that I have gotten quite a few shots with it that just wouldn't have been possible with the EM1.2. Example, we were in this science museum and they had a mirror maze with dim lighting. I had the sony setup for shutter priority to freeze the kids moving around. Was pretty astounded to see that the photos inside this maze were ISO 20000 to 30000, they had a little noise but the detail was still there and the noise is not unpleasant (similar to Oly actually). Sorry, can't post sample bc don't want to put pictures of my friends kids on the internet. But there is no way I could have gotten those on MFT.
I got a grip extender and finished customizing it so the usability and ergonomics are much better now, but still miles from Oly. Perhaps there are more things for me to learn, but this is the big difference. So far, I haven't missed the flippy screen.
The two Tamron 2.8 zooms (17-28, 28-75) are very good. They are pretty similar in performance (with the FF sensor) and even size/weight to the Oly pro zooms. These have stayed on the camera and are, IMHO a game changer for the system bringing it close to the portability of MFT.
What has been hard is making sure there is enough depth of field. With the Oly 2.8's it was rarely a problem to have subjects OOF. So, I have to be careful now and use full manual or aperture priority with minimum shutter selected. If I let the camera choose ISO with shutter priority and it opens up to 2.8 it's hard to capture a scene sometimes. So, it's a good example of when FF and shallow DOF isn't always nice. The sony AF is great but always prefers the nearest object in the scene which can be pretty annoying. Luckily the face/eye detect is great.
I agree that the stabilization is not nearly as good. Nowhere more evident than in video mode. Half pressing the shutter on the Oly starts magic, but on the sony it's just barely good enough to help.
Still not sure what I'll do. Probably keep both bodies and a reduced set of lenses for each.