I have to admit the Cockpit architecture is not entirely clear to me, but at least it seems to allow using SSH as a remote transport, so you don't actually need to install the web stuff on all servers.

GUIs are great for discoverability and observation, but they always make my life harder when I actually need to manage change in a system.

As simple as it is, there's so far nothing that beats plain old text as the source of truth for how things should be; even if you have a fancy API to actually make changes into a system, you'd still want the desired state of that system to be stored as plain old text, so that changes may be tracked and reviewed easily.