I currently own a 6D and an X100s. Have tried basically every mirrorless system and a ton of different cameras within each system over the last couple of years. Everytime I use a 6D or any other DSLR, I just like that it "works". DSLRs just feel like polished image-making machines. Bright optical viewfinder, snappy AF, nice ergonomics, just works.
Most mirrorless cameras I've used just have weird quirks that have detracted from my enjoyment of them vs a DSLR. Of course, these quirks can be offset by the sheer convenience of a lighter mirrorless camera.
I rented a XT1 a while ago for a fairly long period because I wanted to evaluate whether I could go full-time to a Fuji system. The X-T1 had a lot to like about it, I think this was the best mirrorless camera i've used. But still, I just liked the DSLR better. I prefer the OVF, even despite the X-T1's absolutely amazing EVF.
That being said, size isn't a huge factor for me personally. I own a 6D which is one of the smaller FF DSLRs. And I'm usually a 1body, 1 lens type of guy when I go out shooting. Usually it's the 6D and 24-70ii. I don't find that kit overwhelming for the type of shooting I do in terms of size/weight. And if I want to go smaller, that's what the X100s and some of my other small cameras are for. But if one was the type to carry around a full kit when they go out shooting, I can see how a mirrorless system could really add up. Fuji's wonderful fast and relatively small prime lenses would be terrific for this, imo.
So I guess it all depends on your preferences, how much weight savings matter to you, etc.