Not all technologies are good. Not all organisations are good. Sometimes it's one. Sometimes it's the other.
And sometimes it's neither; some organizations are perfectly competent at what they do, but for whatever reason are poorly suited to a particular technology that would work fine elsewhere. (Dumb example: a company overwhelmingly built with Microsoft technologies that only has expertise working with that particular stock has basically no chance of being a good fit for nixos)
Moreover, there are lots of folks having professional success with Nix, and having consumed enough of their stories, I think that the stumbling blocks that the parent identified are faults of their organization and not of Nix in particular. To see this, first replace "Nix" with "Brand X" and note that the complaints are generic to any community-developed software which doesn't have B2B resellers. Then, consider your own experience learning Nix, and note that usability, poor documentation, and a feeling that things are deliberately cryptic are all common to learning any new tool or programming language.
We can comfortably conclude that Nix did not prevent itself from being adopted by the parent's organization. Indeed, it would seem that Nix made itself extremely attractive and adoptable, else it would not have been under consideration!
As an example, I recall trying to build a package for psycopg2 (it wasn't in nixpkgs at the time, and even if it were, for one reason or another we couldn't directly use many packages from nixpkgs), the most popular Python library for interacting with a Postgres database; however, that required me to write packages for a bunch of C libraries that I didn't understand at all, including fishing random header files out of the Postgres source code. No one in our organization including our Nix veterans could figure out how to build it correctly, and it ultimately caused us to move away from Nix (it was among the last straws).
Besides, just because it didn't work for us doesn't imply that there's a problem with our personnel (by several industry key metrics, our devops capability is excellent), but rather that the effort required to implement Nix successfully was greater than the work required to use other tooling. We could use C++ instead of Python for our organization, but just because we don't doesn't imply that our organization is incompetent; rather that Python's tradeoffs are more appropriate for our problems. In effect, Nix creates more problems than it solves for us, which is unfortunate because the problems it solves are really important problems, and many of the problems it creates are utterly unnecessary (add docstrings, use a more familiar expression language--maybe Starlark [https://go.starlark.net], provide and document 'escape hatches' so users can use system dependencies where it's prohibitively difficult to hermetically package things, etc).
After using Nix for a while you start to reflexively shy away from software with low-quality build systems. Nix is not easy to use, but it's best of breed in terms of software supply chain auditability and malleability (anything in the system can be trivially modified or patched). If you can move to an "easy" system, that may be the appropriate trade-off for you, but it means you may be in a domain where these properties are unimportant.
If it helps anyone, here's example where I put my Nix understanding to make it seamlessly usable: https://github.com/takeda/example_python_project
If you use direnv + lorri you just need to enter directory (if not just type nix-shell) and suddenly you have everything you need and the application is installed (try executing "hello" which will execute the python code, if you modify hello.py it immediately takes effect as if you were using "pip -e")
If you call "nix build" you'll get a result directory with "result/bin/hello" that just works as if it was a binary program (don't need to worry about dependencies)
I think nix needs a tooling that does all of the ground work of setting up dev environment for the most popular languages, because it gets really confusing.
I maintain a few open source projects. I have made packages for Redhat, Ubuntu and Arch and updated one Nix package. I love the idea of Nix, but have quit trying to support it and have removed myself as a maintainer.
