Almost -- it's not quite as bad as you'd expect, because nixpkgs has packages for quite a lot of closed-source software, with whatever hacks are required to make it work.
I tried NixOS and dropped it after spending several hours trying to make an experimental FPGA compiler work. The instructions were reasonable, but they expected to have a classic Linux distro: Fedora or Debian-like.
I don't remember the exact set of errors (there was more than one), but NixOS+FHS failed so many times I gave up, and wrote that blog post.
This is the essence: you can't expect application developers to target your niche distro.
Nevertheless community of NixOS developers is many magnitudes smaller than the amount of developers churning out new software, hence once you get off the golden path of the widely or somewhat widely software, the probability of a random thing working without additional elbow grease from the one who tries to use it is indistinguishable from 0, due to NixOS' dialect of Linux not being perfectly compatible with other dialects.
At the very least, documentation for the random thing will never tell you what to do under NixOS, and documentation is very much the part of the software product.
I don't remember the exact set of errors (there was more than one), but NixOS+FHS failed so many times I gave up, and wrote that blog post.
This is the essence: you can't expect application developers to target your niche distro.