Both Plex and Jellyfin refused to import my fairly standard and accurately tagged music library last time I tried, and Plex is definitely opinionated about structure in video libraries.
I don't see the expectation of a standard naming format as unreasonable, given that it's open source and they're fairly short on developers
I'd probably use Jellyfin if it got the basics right and lacked a thing or two, or if its opinionated implementation was limited to trivialities like how Plex refuses to use local images not named cover.jpg. But it's too opinionated, too inflexibly, about too many things, and I think its opinions are stupid, so it crosses the line as far as I'm concerned. Doesn't help that the code is convoluted and I couldn't figure out how to make changes to the way it analyzes files easily.
It still did a great job and Picard nicely filled in the blanks.