I hesitated to weigh in at first because you are asking about the Z6III and OM-1 Mk II, and my experience is with the Z6, Zf, and the OM-1, but I went through this very same conundrum not too long ago, and I believe the cameras in your scenario and mine are close enough for the sake of what I'd like to share.
My m4/3 kit consisted of the OM-1, the 12-40 f/2.8, the 40-150 f/2.8, and the 2x TC. I just kind of assumed that it was lighter and smaller than anything I could build around a Nikon Z full-frame system. I was surprised to discover one day as I looked at my OM-1 with the 40-150 f/2.8 attached and my Z6 with the Z 70-180 f/2.8 that there was almost no difference in their overall size and weight. Ditto the OM-1 with the 12-40 f/2.8 and the Z6 with the 24-70 f/4. And before we get too far, yes, I'm aware that I am comparing a lens with an effective reach of 300mm vs. 180mm in the first scenario, and an f/2.8 lens to an f/4 lens in the second, but let's put that difference aside for just a moment.
That's when I asked myself, "Is there enough of a difference in size and weight in a "full-size" kit - that is, any given full-size body and higher-end lenses - to justify giving up the resolution, dynamic range, and low light performance of the Nikon's sensor?
The answer for me turned out to be "no." The same is true with my Zf, and even more true with the Z6III (which I don't own but have used).
There are endless variables here, of course. For instance, with m4/3, you have more depth of field for a given aperture, so you don't have to stop down and raise the ISO to get an equivalent exposure, which helps mitigate the advantage the Nikons have in the noise department.
Prior to the Zf and Z6III, the OM-1 handily outperformed the Nikon Z bodies in terms of AF performance, particularly in subject detection and tracking. To the best of my knowledge, pre-capture was unique to Olympus before those same cameras came out. But in my experience, the Zf and Z6III perform every bit as well as the OM-1.
In-camera noise reduction in my OM-1 was phenomenal; I rarely used RAW files from that camera because I struggled to do better in post, and the OOC JPGs were beautiful. But the OOC JPGs I've shot with the Zf and Z6III are better still, right up to ISO 12,800.
In the end, I sold my OM-1 and my f/2.8 PRO lenses. My Z6 and Zf and their equivalent lenses weighed no more and were no larger, and I felt as though I was trading dynamic range, low-light performance, and overall image quality for nothing, and I'm considering adding the Z6III to my bag.
Now, if I was looking to build a truly small and light kit based around something like the OM-5 and the f/4 Olympus PRO zooms, that's a different story entirely. This is where m4/3 really shines. So if that's the direction you're leaning, then yes, m4/3 makes sense. But the first item on your list is "High ISO low noise capabilities for low light shooting," and the Z6III is the clear winner here.