For a quick FOV/DOF equivalence here.
Olympus E-M1iii with 12-100 F4: 24-200 mm equiv FOV. Slightly trickier for DOF equivalence, if you want a 4/3 format is a little less than 2 stops difference, if you want 3/2 format is about 2 stops. So worst case scenario is F8 equiv.
Now, because of better stabilization (the 12-100 IS works with the OIS for up to 7.5 stops), if you need more DOF in a light that requires above base ISO, the Olympus can come ahead if you don't have a tripod. In practice is not as easy because there are different generation of sensors.
If you need shallower DOF or higher shutter speed, the 24-200Z is brighter when taking into account the full frame sensor.
I do have to actually test them more though, because I did shoot a little side by side the Z7 with the 24-70 F4 and the Oly combo. I could get much lower shutter speeds with the Oly, but the much higher ISO on the Z7 was looking as good or better than the base Oly ISO, at least without being very thorough.
I've seen a test where the Z7ii OIS was as good as the E-M1iii. I have doubts. I actually did get 5-8 stops on the Oly, while more than 2 stops on the Z7 is challenging. Maybe in a mix with the IS of 24-200 will be better.