Plex logins go through their login server so you’ll also have login throttling and probably other bot protections.

Definitely.

But I think more than copium it’s them understanding their users. It’s advice for people that will figure out how to run Jellyfin but won’t stay on top of updates, setup a waf, use a firewall/reverseproxy to limit access, etc. There are surely a lot of those that just one clicked an installer etc and for them it’s good advice.