So my environment is hard to compare for the issues you're running into.
My library of music has been built over many years, and went through multiple different tools getting the metadata set.
The other issue is, I use both plex and roon on the same library. Roon is amazing at metadata matching, and updates the files. So the success I've had with plex is likely entirely related to roon doing the heavy lifting. But as an example, the artist page brings great additional data.
And, I don't remember ever having to 'fix match' with albums I rip, and that's pretty routine with movies I rip.
To be honest though, if roon worked outside my home network, I'd never use plex for music. It's that much better. I even built dedicated rpi roon boxes for all the rooms in the house so I can use it exclusively for home listening.
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