I prefer Plex for its stupid simple "press here to share your library with your family remotely." And before the Jellyfin folks have an aneurysm, yes I know I can "jUsT uSe a ReVeRsE pRoXy" but I'm a busy guy and frankly lazy. So if Jellyfin wants wide adoption, it needs to make library sharing stupid simple.
This would be huge, one of the biggest draws to Plex for me is being able to use a single account to watch content across all my friends servers from any Plex UI (be it the hosted one at app.plex.tv or the copy hosted with each Plex server)
If you're waiting for Jellyfin to run some kind of relay like Plex, you'll be waiting a long time. That takes a lot of money to upkeep, and the demand for people who self-host FOSS and then want to depend on an external service is very minimal, certainly not enough to sustain such a service. I'd recommend just spending a weekend afternoon learning how to set up Nginx Proxy Manager and being done with it, the GUI makes it very easy.
The way Plex achieves the sharing is very convoluted and intrusive. You basically go through their servers and show them everything you have and everything you and everybody you share with are watching.
Most people who pick Jellyfin do it to retain control not give it away.
I like plex better but damn is it bloated, had to take a almost an hour digging through settings to turn all those plex features off. Now it feels more back to basics.