Doesn't have to be that way though. As discussed here recently, a basic local agent like Claude Code is only a couple hundred lines of code, and could easily be written by something like Claude Code if you didn't want to do it yourself.

If you have your own agent, then it can talk to whatever you want - could be OpenRouter configured to some free model, or could be to a local model too. If the local model wasn't knowledgeable enough for sysadmin you could perhaps use installable skills (scripts/programs) for sysadmin tasks, with those having been written by a more powerful model/agent.