Self-Hosted Main

First, lets get all of this cleared up.

Plex came first. It was a fork of XBMC(which became Kodi).
Technically, most users could just run Kodi with a central library database and get most of the same benefits. The problem is that would primarily work for local players and wouldn't work well for remote operations.
Plex got ridiculously popular back in the day because it had the same attitude as Kodi when it came to addons. There were a ridiculous number of addons that essentially made piracy seamless. So, Plex was a popular option for people who wanted to pirate movie streams, organize media, and do a lot of other things. This is when Plex started to surpass Kodi in popularity.

Emby came second, as an open-source alternative to Plex. One difference was that it never really allowed plugins in any significant way and therefore didnt get as popular. When Emby went closed source a few years ago, some people forked it off into Jellyfin.

Jellyfin came last. Plex and Emby had closed source their products primarily because of remote transcoding. So for quite a while, the transcoding on Jellyfin was trash. It also had a number of weird quirks and bugs. It was fairly half-baked. I personally bought Plex lifetime after Jellyfin came out because Jellyfin wasn't mature and Emby cost money too.

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At the end of the day, Plex has actually gone backwards in features because they are trying to be a more acceptable product. This means fewer mods for piracy features and they've killed some of the other features while adding in their "free streaming" options and some other questionable decisions.
But Emby has died and Jellyfin is still a poor substitute. Can you use Jellyfin? Absolutely. Wouldn't even blame you if you do it. You can also run Kodi as described. But I absolutely felt it was worth it to stop fiddling with Jellyfin and just run something that worked and rarely crashed, had errors, etc.