Plex is great. There's rock solid and then there's rock solid to the extent that my spouse and family members can all use it with no support calls to me. My dad was able to download movies to his iPad for a flight to NZ all on his own.
Yes, they keep adding cruft, I just ignore or hide it. That said, I didn't know I wanted Plexamp until they gave it to me, and now I love it.
If you like PlexAmp then you might be interested in Prologue [0] as well. It’s not a first-party app but it’s audiobook app that uses your Plex server as a source. So you can have a library of audiobooks that it pulls from.
I buy all my audiobooks on Audible, remove the DRM, then put them on my server so I can use Prologue instead of the default Audible app. Yes, you give up WhisperSync but I rarely use that anyway.
[0] https://prologue.audio