Well at least it's not a pile of hardlinks like apple's time machine. Actually that might be an interesting option for an OS... constant versioning.
FWIW, you can repack the nix-store to be a pile of hardlinks...
Isn’t it mostly environment variables?
Arguably the most important part of Nix is the fixed hashed output of everything, and these fixed /nix/store/hash-lib entries being used for dynamic linking.