Well, well, well. That was highly instructive: I took out the X-E3 alongside the Z fc today - and things turned out rather unexpected.
First and foremost, while Fuji has played the vintage game for a while now, Nikon has done a great job - I personally find handling the Z fc at least as satisfying as the X-E3, and I enjoy shooting with it more. The Z fc does a couple of things much better than the X-E3 (I'm aware that this is a last-generation camera - newer Fujifilm cameras may do better): It's quicker in most respects, and more straightforward whenever you need to adjust settings. The EVF is miles ahead of the X-E3's smaller and (something I hadn't noticed before) rather dim and overly contrasty unit. All things considered, shooting with the Z fc feels more natural, faster, less restricted by the behaviour of the camera - more confidence-enspiring, less cluttered. This surprised me quite a bit - because on paper, the X-E3 has a control scheme that should suit me better, but this doesn't bear out in use. The two cameras are different enough to make a direct comparison somewhat tricky, but I clearly preferred the Z fc over the X-E3 this time around. I dare say that the Z fc, while clearly a mid-range camera (maybe even entry-level in some respects), performs just as reliably and fluidly as its more ambitious FX stable mates - something that the Z 50 does almost as well, yet the Z fc is a tad swifter still. The X-E3 is a good performer - but no match for this kind of high-octane responsiveness.
The X-E3 shines at one thing - albeit an important one: The images you can get from its (older!) sensor are really, really appealing; I find Fujifilm's colour science way better than Nikon's. This doesn't mean that with some work, I couldn't get similar results - but if attractive images are required with minimal work, the files from the X-E3 are (for me at least) a clearly more desirable starting point. That said, you mostly see the differences if you evaluate similar images side by side - when all I have are files from the Z fc, I am happy enough with them and can get pleasing results with acceptable effort; and high ISO shots from the Z fc (and Z 50) are basically better from ISO 1600 onwards. However, considering once more the fact that the X-E3 is a couple of years old already and newer Fujifilm cameras will beat *it* in most respects (maybe except high ISO capability, though), the advantage of having access to such gorgeous files is considerable.
The comparison of the two lenses I took - the 28mm SE and the 23mm f/2 - was very interesting and somewhat revealing as well. Long story short: The 28mm holds its own against Fujifilm's venerable 23mm; what's more, it's clearly better at closer distances, at any aperture - sharper, with less aberrations. At medium to far distances, the quality difference is negligible, though, and by f/5.6, the Fujifilm performs as well as ever. Its biggest weakness is the wide-open performance near its minimum focus distance - the Nikon dominates that contest with ease, while allowing me to get even closer. I still find framing with the 23mm easier (I'm a 35mm FoV guy), but the slightly narrower perspective of the 42mm-e is very useful, too - and this obviously is a matter of taste and shooting opportunity. All in all, what Nikon has delivered optically is extremely impressive; obviously, when it comes to build quality, the Fujifilm lens remains clearly superior in every respect, and as the incurable traditionalist that I am, I prefer its physical aperture ring. That said, the 28mm gives Fujifilms 27mm f/2.8 a run for its money - yes, that lens is smaller, but its AF motor is less confident and clearly noisier, and while no slouch, it can't compete optically. So, while I still see the 23mm's distinctive, if diminishing value, the 27mm f/2.8's size remains its only real asset ...
Where does this leave me? Well, depending on how the market develops - especially as far as third-party lenses for the Z mount are concerned -, I can see myself selling the X-E3 sooner rather than later. I have thought about this for a long time already; in spite of the many good points of the camera and the mature system it belongs to, I don't think I would miss it (much) - and that is true now; it may get even more obvious once a couple more small primes for the Z fc become available. I have been looking into the Viltrox f/1.4 lenses, but am not quite sure I want to go there - from what I can see, they're good, but clearly not as good as Fujifilm's offerings - and those are beaten by the rather pedestrian 28mm SE already in many respects ...
Maybe I should take a page out of Andrew's book and try the Z 35mm f/1.8 S ... that lens works wonderfully on the Z 50, anyway, so I know what to expext (at the very least!).
M.