That's the nice part, as an admin you are familiar with the complexity and use it for good. As a user, you never have to see it. (And you can even have some freedom for installing apps using flatpack/snap if needed.)
How would you role out the same config to thousands of Arch systems? Sure Valve does it, but I still think that is a "bolted on top" solution. Bootc could be another option though, but Nix solves reproducibility more elegantly, imho. Nix went back and asked "how can this be done better", where many modern solutions took what was already there.
The problem with Arch is that configuration is by hand so you have to do it every time. With Nix you configure it once and then you can deploy it anywhere. Also it's pretty much impossible to break since the system is immutable and you can boot to a different revision any time.
I can imagine. Those are often the sort of projects that struggle to put a one line description of what they are on their homepage. I inferred it was an OS, inferred it was Unix adjacent...but no answer on the rest. It could have been BSD or open Solaris based for all I could tell.
Windows also is unnecessary complicated for a singular install but works kinda well for a network and central administration by someone who likes to read the docs (or whatever you read for windows)
Probably has its uses, tried it twice myself and both times were a lot of struggling.
For me even Arch was easier to configure than Nix.