While you're technically correct, docker compose uses yet another process supervisor (the docker daemon) while systemd is already capable of doing that. This is probably what the author meant by 'external dependency' - not the need to install compose separately. Quadlet delegates the supervision to systemd daemon, eliminating this duplication of supervisor functionality.

Kubelets in K8s also have similar duplication of supervisor functionality. Perhaps this is a good place to mention the Aurae runtime [1], which is designed to replace systemd, docker daemon, kubelet, etc on dedicated worker nodes. Sadly, its chief designer Kris Nova passed away recently in an accident. I wish the rest of the team the strength of carry her legacy forward.

[1] https://aurae.io/

Not quite, docker-compose is shipped separately by Docker as docker-compose-plugin. The plugin can then be reached with the subcommand "docker compose".

However, I agree with your sentiment. It's basically a part of any modern Docker installation now. Calling it an external dependency "like watchtower" is not a fair comparison.