It's a bit of a snore. My tongue-in-cheek rejoinder:
I prefer the improved ability to critical focus in dim light and with ultra-wide lenses given by the Olympus E-M1, or Leica SL EVF over ANY optical SLR focusing screen, never mind the additional focusing aid provided by focus peaking, or live histogram view and exposure simulation for judging proper exposure.
I have excellent Leica lenses in focal lengths from 15mm to 500mm focal length, all of which perform beautifully on my Leica SL. Similarly, I have excellent Olympus and Panasonic/Leica lenses in focal lengths from 22 to 560mm (equivalent) for the Olympus E-M1. My six Nikon lenses are no better.
3. Battery Life
I have never run out of battery life during a shooting session from a single battery in any of the mirrorless cameras I've been shooting with since 2009.
4. Focus Speed and Accuracy
My preference is manual focus, and I usually beat any AF system's accuracy when shooting my typical subject matter.
5. Controls & Ergonomics
My Nikon D750 feels like a Magic Wurlitzer of buttons, dials, sliders, and menu options compared to my SL. (So does the E-M1, for that matter. :-)
6. Buffer Performance
I shoot in single shot mode 99.9% of the time. Both my cameras far exceed any need for buffer performance I might have.
The DNG files out of the SL at the cameras defaults are as neutral as the NEF files out of the Nikon. In fact, they're more malleable when editing.