There's no good reason for any folder structure to hobble a media browsing frontend. There are multiple frontends I've tried for my personal library of ebooks (mostly Humble Bundles of software/hardware books), and a number of those frontends have an option that's basically one book per folder (i.e. all identically named files in that folder treated as different versions of the same book... epub, pdf, etc) and folders above that can be whatever you want. BookOrbit[1] supports arbitrary folder hierarchies and Readest[2] supports at least one level of intermediate hierarchy.
In the context of existing software counterexamples, Jellyfin's delicate sensitivity to folder meta-structure is a regression from the baseline expectation. But I'd agree that ultimately folder naming requirements for the media items themselves makes good sense.
> In which case, enjoy your UI being a series of nested folders.
When the Jellyfin UI reflects those nested folders, I can tell it to only rescan a specific subfolder when I add a movie, rather than checking the whole library for new content. Folders and hierarchical structure are objectively useful, though our search-addled brains make that less obvious than it used to be.
[1]: https://bookorbit.app/library-file-structure/#grouping-folde...