Last October I ditched my Canon 100D in favour of the mirrorless Canon M5. And as much as I love that Camera, there are definitely some flaws in the System, most of them I have my own solution for.
The biggest Pro of going Mirrorless for me is, by far, having an EVF instead of an OVF. In the latter days of my old Canon 100D, I started relying on Live View shooting more and more, especially in more challenging Lighting Conditions.
Another huge Advantage is Autofocus. The old Camera only had 9 Viewfinder AF Points, and that was a real Problem for me, as I mostly rely on good Autofocus for my Photography. With my Mirrorless M5 I can focus pretty much anywhere I want with the help of its Touch & Drag AF system. Its Dual Pixel AF is also way better for Video than the 100Ds Hybrid Af.
The biggest downside of the Canons M System would be Native Lens Selection. Canon only offers 8 EF-M Lenses at this time, and there are just about 40 Third Party Lenses, few of them offering Autofocus. And while I happily use Canons EF to EF-M Adapter, that Solution is not ideal.
Another Thing is the Battery Life. While it is certainly better than the Life View Battery Life of the 100D, it definitely lasts shorter when shooting through the Viewfinder. But I always have Spare Batteries with me anyways.
The only Difference in Image Quality comes from advancements in Sensor Technology though. More Megapixels and a higher Dynamic Range definitely make a difference. I also use mostly the same Lenses as before the Switch anyways, so I do not notice much Change in that Regard.
All in all though, I definitely prefer Mirrorless Cameras over DSLRs. They are just so much better in my view and will be the Future of Photography. And while I love my old analog SLRs, I will never go back to a DSLR.