It's significantly uglier and it also skips the helpful headers / sections in the systemd INI files. `[Unit]` and `[Service]` and `[Timer]` represent different layers of execution. Many Nix people got used to the horrible syntax of Nix, I guess? I still find Bitbake significantly more palatable than Nix.
I do appreciate build-time checking but I think this can be solved at systemd side as a separate tool just as effectively.