Ya I'm surprised that people are advocating for Plex these days especially in a self hosting community, it's overbloated and mostly exists to force their FAST service down your throat
Plex has to be one thing where I like the bloat. It makes it feel like a fully featured streaming service that I control instead of just a fancy looking video folder.
I'm assuming cause it works good enough for most that the incentive to change it nearly none. Kinda the same deal with moving from reddit, works good for the use case that open stuff might be worse.
Currently using symfonium, does everything I need at least. Can't speak for plex since it been years but it has most of the things you need, offline playback, playlist downloading and syncing, casting, supports transcoding etc. Plus it works with plex already so you can try it out (it's free for a week then paid iirc but it's well worth imho)
The player I use for it is symfonium and it can do instant mixes. Genre tagged based tho, so it can be a little wonky but it gets the job done for the most part
finamp is missing enough features to me to make plexamp worth paying for to me (not automatically switching to transcoding on mobile data, not supporting opus transcodes)
Plexamp is really great software -- the various methods of randomizing means I'm re-experiencing parts of my music collection like new, and connecting tracks to other tracks that I'd never put in the same playlist.
Dispointed though, I use exactly the same music set stored on my phone and also on nas drive. Yet sorting doesnt always put the album together and the search doesn't find all of the artists songs.