So What is the Mirrorless problem?
My problem is that the Fujifilm XT2 electronic view finder is so good, that I often forget that I am actually using a DSLR. It looks that real, and because the DSLR view finder does not show expsoure in real time. My exposures are often incorrect with the DSLR.
Here is another way to understand it
With the XT2, I have set it up that I am basically shooting manually. With the back dial changed so it controls my shutter speed. I set the aperture (on the lens) and dial in the ISO. Then all I have to do is change the shutter-speed to overexpose or underexpose a photograph. And because I see this exposure changes in realtime on the image in the electronic view finder. I make adjustments simply with the shutter speed dial.
With the DSLR, I don’t see these change on the image in my viewfinder. Because the image in the view finder is reflected straight up from the lens to the view finder by the mirror. So when you make exposure adjustment on a DSLR, you don’t see these changes. Till you look at the photograph afterwards. Which leads me to my next problem. I am not chimping with my XT2. So I am out of the habit of checking my exposures after I have taken the photograph.
I only really notice these incorrect exposures away from the scene or on my computer much later. With wildlife photography, there is not such thing as a retake!