I'm not a pro, but did switch from 5D3 to XT2 and XPro2, primarily for weight.
The Fujis certainly deliver in terms of weight - not just because the bodies are smaller, but the glass is too (no magic here, it's just sized for cropped sensors, so can be smaller).
Image wise, I have no complaints, but I don't review at 100%. I had no complaints with the Canon on the same basis. I was (and am) very happy with the output from both.
I do tend to use the Fuji jpegs more than the raw now - I don't think that's because the jpeg files are magical, it's just there's more focus / attention our there on internet about in camera settings, so I paid more attention to them on Fuji and it means I spend less time on the computer, whereas on the 5D3, I didn't even bother shooting jpg as that was the perceived wisdom at the time. The big advantage of mirrorless over DSLR here is what you see is what you get - the EVF reflecting all aspects of the shot means I'm much more adept at dialing in compensation when I need to.
The another big advantage of mirrorless for me has been Manual Focus capability - it's excellent and far exceeds the 5D3 using OVF. I've got to play with a lot of old lenses with adaptors, which is fun, and I have no fear about manually focussing any lens of needed, although I do use AF 99% of the time with lenses that support it.
Last big plus - the dials - especially the aperture ring. I tend to shoot Auto ISO, Auto Shutter and manual Aperture - adjustment is so natural I don't even think about it. Equally simple to switch to manual shutter etc. It's a well though out system and soon becomes second nature.
What I miss? The AF, while more than good enough for my current use, isn't as good as the 5D3 when it comes to fast moving, unpredictable subjects (mainly kids football for me); My kids don't play anymore so it doesn't matter. AF in general use feels fast and accurate - it does depend on the lens - newer lenses are very very fast, but then tend only to have f/2 max; the older lenses, are a little slower as a rule, but nothing to cause concern.
The other thing I miss is the 'magic' combo of the 5D3 and the 135L lens - It just produced some awesome images. I have the 90/2 which is the fuji equiv and while it does produce great images, it's just not the 135. Can't put my finger on it, but it's not down to the sensor size alone - must be some funky glass in there somewhere.
Finally - ergonomics - the XPro2 layout is superior to the XT2 in my mind within the Fuji world, but if you've walloping great hands, they will both be small to hold compared to the Canon - good thing in terms of bag size, but can take some getting used to.
All that said, I take a lot more pics with the Fuji than I ever did with the 5D3 simply because I have it with me more often. Important distinction here thought is as a hobbyist, I can choose whether I take a camera or not, so weight is a factor in that. As a Pro, I guess you will always have a camera when you are working, so that choice isn't really relevant to you.
