Up until the last few days I would have said yes, I am happy with my mirrorless system.
I just did an intensive three-day multi-model vintage fashion shoot. I had eight shooting areas set up, and was flitting between them.
This client needs web images, and I know they can handle Canon files and have liked Canon colours before now. So as on previous shoots with them, my main workhorse camera was a Canon 7D (mark one) with 24-70 mm f/2.8 L (mark one). A bit primitive by modern standards, I thought. For my own website I usually shoot either Hasselblad H3D31ii or latterly Sony A7Rii. The Hassy is out of the question for this client (I'm not teaching them the ins and outs of Phocus workflow, and if Moire happens, it can be intolerable for this client's clothes).
But because I needed a backup system, I brought along the Sony and shot with it for some sets.
And oh my god it was a reminder how far Sony have to go to sort out ergonomics and user interface.
It was a bit of a revelation how much faster and more confidently I could work with the Canon - a camera which never actually was my workhorse (I bought it for video at the start of the dSLR revolution, to replace a 5D Mark I which had been a workhorse but which has different control layout). The Sony has been my go-to camera for well over a year now, with me racking up maybe 100,000+ shots on it. You'd have figured that the camera I use daily would seem more familiar than the old one I'd not shot with in almost a year, wouldn't you? But it didn't.
Now the results of the Sony are duly impressive on the technical front, no doubt. I likely won't be printing any of the 7D shots to 24" x 36" for gallery display.
But bloody hell, it was a lot easier and more productive to shoot with than the cussed Sony, whose user interface still pretty much guarantees menu hunting and many more missed shots. The Sony has a mode for everything, but to get the shot you need to change to the right mode. The model starts to move or do some walking shots? You'd better switch to AFC and the right sort of AF settings and get your zones sorted. If you press and hope, it'll mess up. The Canon has lots of modes too, but my experience was that in use, if I forgot to change over when the model stared to move, the camera would do a pretty workmanlike job of getting it right regardless.
The Sony felt like a fussy highly-strung old maid by comparison. Capable of excellent results. But if you don't get the settings just so, it'll sulk and may not shoot a single usable frame until you change modes. Oh, and you won't get through a day's shoot on a single battery like you will with the Canon either.
So the Sony remains a technical tour-de-force, with great lenses, a lot lighter than the Canon (essential for mountain photography) and very many fantastic features.
I'd dearly love someone to take the same A7Rii innards into a completely redesigned camera. Like completely rethought and re-engineered layout and physical design and everything.
The shoot has made me rediscover the virtues of a solid dSLR with a decent zoom lens (the 35-135 equivalence of a 24-70 on APS-C is just perfect for people/fashion photography). I'm keeping my Canon kit, and I will look at a 7D Mark II when I finally burn out the shutter on the 7D.
Of course, mirrorless systems are just getting going whereas the dSLR has 15-ish years of development, and borrow a lot of tech from the film era. I think there's more strengths and weaknesses in the mirrorless systems: I much prefer the UI of the GH4 to that of the Sony, but the GH4 can't compete with 42 megapixels full frame and dynamic range of the Sony, for example. dSLR's are Swiss Army Knives- do anything, but not quite as well as an actual screwdriver or saw. Mirrorless systems are more like a single-purpose tool. It'll cut you angles at exactly 90 degrees or exactly 45 degrees, but it won't let you bodge through when you want 63 and a half degrees.
It confirmed my prejudice that if I had to pick just ONE camera system to shoot everything with, I'd still go for a Canon dSLR, regardless of how it all looks on paper.
Cheers, Hywel