What about the XT3 versus the XT4? The big deal is that the XT4 has in body image stabilization. There are other differences, but this is the main thing.
Fuji is interesting in a number of ways. First of all they don't make a full-frame camera. You either go with APS-C or you go to their medium format bodies. Part of the angle is that they view APS-C as a serious camera, whereas Canon and Nikon offer APS-C as a "amateur" camera with the expectation that the serious professional will go full frame. This not entirely true. The Canon 7D was always a serious APS-C camera.
Fuji also has an interesting design aesthetic. Their mirrorless cameras look like old film cameras with sharp lines, polygonal shapes, and knobs instead of menus. If you buy a camera for looks this is important of course. But beyond that, the ergonomics of their cameras will be different than say a Canon or Sony.
The X-T4 has a 26 megapixel sensor, in body stabilization, 425 focus points, and can shoot 20 frame/second bursts. It has a 3.7 megapixel EVF and will shoot 4K video at 60 fps. They claim a battery life of 500 shots. Price is $1400, so it is reasonable to compare to the Canon RP.
In my case, I don't care about video and really don't care about fast burst shooting.
Fuji uses their own "X-Trans" sensor which has a different layout than the Bayer pattern in most other cameras. Just what difference this really makes in photos I don't know. The trick is penetrating past marketing claims.
I tend to think that jumping ship from one brand to another is foolish if you have any investment at all in lenses. You are better off waiting for Canon to bring out a new camera body than jumping to Nikon because the current Nikon body has more megapixels (or whatever is luring you to make a switch). Make a good choice up front and stick with it. Learn to improve your skills with what you have rather than chasing the latest hot trend.
My friend Howard has the following lenses he uses with his XT4 --
The 18-55 that came with his XT3 (he says this lens is wonderful).
A 55-200
A 60mm f/2.4 macro
Three manual focus Nikon lenses: Nikkor G f/1.8’s: 35, 50, 85 full-frame lenses. He uses a Fotodiox shift/tilt adapter.
Tom's Digital Photography Info / [email protected]