....Hi Phil, you have probably read my enthusiastic posts about the M5 when I first had it. I am still enthusiastic about it but of course I have now had more time and use to learn its limitations, but these are only limitations in the context of my personal use.
The most fundamental aspect of my particular use is that I
ONLY mount EF lenses on it and all L lenses except a 40mm 'pancake'. So, I have nothing to contribute regarding other lenses mounted on the M5.
Regarding image quality, if you inspect my 'EOS M5' Album on Flickr I am confident you will agree that the IQ is absolutely equal to crop-sensor shots on the 7D Mark II (and probably 80D which I don't own).
Here is a link to my 'EOS M5' Album:
https://www.flickr.com/photos/114775606@N07/albums/72157683996949495
Personally I am still not 100% about EVFs but otherwise I find the physical controls just a little bit fiddly when I switch with the EOS D-SLR larger bodies. But that's the compromise I accept to then be able to gain the more compact size - There's no such thing as the perfect camera!
So my conclusion is because the IQ potential is so high on the EOS M5, it doesn't make sense
NOT to mount high quality EF lenses. This is opposite to how some folks think about the M5.