ive been using kodi (xbmc was better moniker) since google killed sagetv. i recall attempting plex, but it seemed to lack some open/extensibility (its been awhile).
i have a side project i want to make as a modular plugin generating a cable layout with original air orders and networks/channels... kodi seems most optimal, but ill admit its been a long while since i looked at plex.
There are not tons of themes. There's like 5 of them for any major release. Not even the same ones usually. Sometimes new devs resurect an old theme, and port it to the current release.
It has been years of struggle to keep it looking decent. I'm especially fond of Arctic Zephyr. It's not really a single theme, but a framework that allows you to make your own UI, without typing a single line of code. Multiple forks has emerged and died over time, and now I'm just ignoring the osmc update prompt until some brave soul embarks on a journey to properly port it again.
Also, kodi and plex are different things. Jellyfin would be an alternative to plex.
If you can't find it I can upload original skin files for you plus a link for proper setup (setting can be overwhelming). I also use tinymediamanager to scrape content and have everything completely locally.
Kodi is way more customizable than Plex, Jellyfin or Emby. You can't really change much other than the categories you want it to show and the order their in. They're all dead simple interfaces meant for anyone from a 7 year old to a 70 year old.
If you take a few minutes and dive into the setting of a Kodi theme you can literally make it do whatever you want. It was originally written as a dashboard for the original Xbox, so customization and usability was at the front and center.
It's like comparing a semi truck and a hatchback sedan, they're both vehicles but they server different purposes.
Sure, but the thing is Jellyfin and Plex both work pretty close to what I want without having to customize anything. I'm happy for everyone that likes Kodi, it's just not for me. I've used Kodi on and off from back when it only ran on the Xbox as XBMC. I know what it's capable of. I just don't want to put that effort into it.