NixOS is anything but a light abstraction (I say this as a NixOS user).

Tbh it feels like NixOS is convenient in a large part because of systemd and all the other crap you have to wire together for a usable (read compatible) Linux desktop. Better to have a fat programming language, runtime and collection of packages which exposes one declarative interface.

Much of this issue is caused by the integrate-this-grab-bag-of-tools-someone-made approach to system design, which of course also has upsides. Redhat seems to be really helping with amplifying the downsides by providing the money to make a few mediocre tools absurdly big tho.

How is it not a light abstraction? If you're familiar with systemd, you can easily understand what the snippet below is doing even if you know nothing about Nix.

    systemd.services.rclone-photos-sync = {
      serviceConfig.Type = "oneshot";
      path = [ pkgs.rclone ];
      script = ''
        rclone \
          --config ${config.sops.secrets."rclone.conf".path} \
          --bwlimit 20M --transfers 16 \
          sync /mnt/photos/originals/ photos:
      '';
      unitConfig = {
        RequiresMountsFor = "/mnt/photos";
      };
    };
    systemd.timers.rclone-photos-sync = {
      timerConfig = {
        # Every 2 hours.
        OnCalendar = "00/2:00:00";
        # 5 minute jitter.
        RandomizedDelaySec = "5m";
        # Last run is persisted across reboots.
        Persistent = true;
        Unit = "rclone-photos-sync.service";
      };
      partOf = [ "rclone-photos-sync.service" ];
      wantedBy = [ "timers.target" ];
    };