No, they really don't. I manage a fleet of hundreds of servers with NixOS. Surprisingly huge companies are using Nix, feel free to look around. I can build for 4 different architectures, with identical system configurations, from a single readable codebase.

I've actually never even heard this particular complaint. What exactly have you heard about problems with nix "at scale", or are you just exaggerating what a "learning curve" is again?