I agree. But we are keen photographers with an eye to getting the maximally pliable image. Most clients do not care about the technicalities and it comes down to 'do I like the image'. We get carried away with gear and technicalities to an extent that passes the client by.
Quite a few professionals will disagree. E-M1 mkii with 7-14 f2.8 versus a 5D4 with 16-35 f2.8. Or even EOS-R with 16-35 f4. Then add a couple more lenses (such as a 60mm macro and wide primes and even a standard zoom) plus the filters and spare batteries and other paraphernalia then lug it all for 6hours cross-country.
I agree that it seems other mirrorless marques are narrowing the gap but the gap is there - and when it narrows more I suspect that those shifting to MFT may switch back and get the best of both worlds but we aren't there quite yet.
I presume your argument here is that the Olympus MFT system has better dedicated lenses than an APS-c system ? From my experience in comparing these the larger sensor of the APS-c still wins hands down when it comes to large output. Also I've found that these small, high density sensors still require a good steady tripod to optimise their output.
Perhaps you can point me towards some of these professional landscape photographers who are using MFT and I'll be able to get a better understanding.