Hi,
Well, all these things are simply tools to get a job done. It's a matter of choosing which tool for the job at hand. And it isn't as clear cut as to just what the differences are with digital as it was with film.
Personally, having come from the film era, small formats were quite limited when it came to print size. And the smaller the format, the greater the limitation.
With digital, my first one was a Nikon E2 and that was very, very limited and sported a 2/3" CCD. It was aggravated by being behind a set of reduction optics within the body. So it was difficult to tell just how well (or not) the 1.3 MP sensor worked. So, toss this one into the bit bucket.
What came next for me was APS-H at 6 MP in a Kodak digital back on a Nikon film body. Much improved over the E2 but still rather limited. It was fine if you had a lot of light and weren't in any hurry. Frame rate was one shot every two seconds.
Next up was the Nikon D1, which lost resolution down to 2.75 MP but gained significantly in the operational speed department. I used a D1 or D1H for a long time alongside Kodak 6 MP units. I didn't get a full frame digital until 2018 and I started digital in 1999. 19 years.
What we have here are issues which were not really dependent on the format chosen but the early state of the art. The largest issue being figuring out the field of view for those 135 format designed lenses on the various sensors. That was why Nikon and Fuji had collaborated on the E series (aka DS-5xx at Fuji) with those optics inside the body. It gave 135 format FoV on that small sensor. Mostly.
Once we get into later times, we have lenses designed to go with the sensors and so all that figuring regarding just which lens to use goes away. And, presumably, said optics are optimized for the sensor size better than slapping a 135 format lens on.
These days, I do most of my shooting with either a 135 format sized sensor (aka full frame) or a slightly smaller than 645 sensor (44*33mm) in a medium format body.
I have a couple older APS-H and APS-C bodies still, used for specific purposes. Picking the tool for the job. And, not yet mentioned, including a cell phone cam - whatever format that is.
I have not had a m43 sensor camera, but expect I'd get certain jobs done just fine with one. And then I'd be shooting other jobs using the other cameras.
All that said, I don't see me getting an m43 unit given I have all these others around. But, I'm not going to say Never. Hard to see, the future is!
And I don't see anything to argue about.
Stan