I think I hear in your question an implicit assumption that the collection needs to be accessed the way it is organised, and organised in a strict, consistent hierarchy.
Here’s an alternative view: classical music works best when it can be accessed by different ways when the mood strikes you: chasing down everything by a singer one day, comparing recordings of a work another day, listening all the way through a particular opera recording on another day. That means you need a tool which can search through your music collection according to multiple attributes — composer, main performing artist, composer, work, whatever. Walking through a strict, consistent hierarchy cannot give you that flexibility. So, find a tool which doesn’t limit you to that.
Yes, the music files need to be stored in directories, and directories are easier to manage if they are in a strict consistent hierarchy. But if you have a flexible tool for searching, it doesn’t matter nearly so much what the file storage structure is.