I was not aware of the Nikon Z fc. I had a quick look and I really like the aesthetics I must admit. However, I was playing in Camera Size Comparison
and 'put a 38(?) mm lens on it and the lens appears relatively large compared to the Olympus/Fujifilm lenses. Is that right?
That was probably the Z 28mm f/2.8 which is a FX (FF) lens but works very nicely as a 42mm-e on the Z fc, SE (special edition) version is one of the kit options for the Z fc. There's only one super-small prime for the Z system, the recently released Z 26mm f/2.8 pancake I mentioned before in this thread. If you want/need small,
and, to a degree, Fujifilm are clearly the better bet - that's one of the main reasons I keep
around. That said, even though it may look kind of bulky, the Z 28mm f/2.8 isn't a huge lens, nor is its Z 40mm f/2 stablemate - and both are FX lenses as well as optically quite good for their modest price, too. Except for a couple of zooms, there aren't any dedicated DX/APS-C Z lenses by Nikon yet; only a single DX prime is on the roadmap, as of yet (an interesting one for me, though: 24mm). S Line primes are quite a bit bigger, though optically generally fantastic, so you basically get your money's worth if you can stomach the size.
Anyhow, if you're a prime shooter, for the time being, both Fujifilm and of course
offer a lot more options, and very interesting ones, as has been pointed out. I especially love my super-wide and fisheye options, the Laowa 7.5mm f/2 and Samyang 7.5mm f/3.5; both are optically strong, small, well made and affordable.
The Sigma Contemporary f/1.4 primes will become available for Z mount soon, though. Definitely very interesting - I've owned the 30mm f/1.4 before for both
and E mount and found the lens very rewarding; on the Sony A6000, it was my go-to EDC lens. And as Tili indicated, the 56mm f/1.4 is a great lens, and small to boot. I'm on the fence about the 16mm because it's so large, though. And I don't consider the 30mm a small lens, either.