Hah I just wrote something similar today to periodically push backups to another server from my NAS.

I agree the systemd interface is rather simple (just translate nix expression to config file). But NixOS is a behemoth; Completely change the way how every package is built, introduce a functional programming language and filesystem standard to somehow merge everything together, and then declare approximately every package to ever exist in this new language + add a boatloat of extra utilities and infra.

I was referring to working with systemd specifically on NixOS. But yes, the Nix ecosystem is not easy to learn, but once it clicks there is no going back.