This is an issue with nixpkgs not nix. Google could've just bootstrapped their own nixpkgs from scratch if they wanted to, see Guix (not a perfect example but still). Creating a whole new tool is still completely unnecessary
Nixpkgs is more valuable than Nix at this point, but also quite vulnerable. In practice it has worked out reasonably well so far, I don't know of anyone who got "owned" because of Nix.
Not anymore with the introduction of dynamic derivations (experimental)