I think that this structure reflects actual way data is stored in empeg. PARENTS tags would have to be calculated by crossreferencing. This way they just traverse the tree (taking care to output a particular list or tune node just once - after it has been first referenced).

It's difficult to make playlist structure dump human-friendly without repeating list or tune data - FID reference means little to human reader. Can be done, I think, with a bit of redundancy. But then, human-readability is just secondary property of XML - the main being ease of parsing and certain self-documentation.