I just bought a GX9 5 years after selling my whole system cause I missed the form factor so much. M43 really is the best compromise between size and image quality imo, with the caveat that I'm not a professional. No other mount lets me casually EDC an 80-300 equivalent lens.
There's Esquisse (https://esquisse.camera/) trying to step up, but it's still in the very early stages.
A lot of the Leica-branded lenses have an aperture ring that doesn't work on Olympus bodies. Besides that, both brands have proprietary lens + body stabilization that only work if the lenses and bodies match.
There's Esquisse (https://esquisse.camera/) trying to step up, but it's still in the very early stages.