This is true. You create a plex account, which allows you to log in from anywhere and will give you access to your media. The real problem is that if your outside internet goes down, you can’t log into your own server.
You don’t (hopefully) run admin account on your and family’s phones or TV
let’s be honest: Even if this account was logged into some device that gets lost or something… what could happen? None of the apps can actually do any admin stuff. Even if it could: What harm could anyone do really from within the Plex container?
The real problem is that if your outside internet goes down, you can’t log into your own server.
That’s not true. You can specify IP addresses that are allowed to connect without authentication, eg your local network. So in the event of an internet outage you can still watch tv.