There is a simple and somewhat manageable workaround for this but as you said, "inelegance" is definitely the right word to describe this nonsense:
Append the name of the book to the Album Artist tag. This then will create a folder for each book in the iTunes Media/Audiobooks folder.
The Album Artist tag does not show up in Audiobook mode if it is blank though so the Media Type has to be changed to Music first (File>Get Info>Options>Media Type>Music>Ok). Going then to Music mode, select your book, Get Info, add the new Album Artist tag then switch the Media Type option back to Audiobook.
Example:
Artist: J.R.R. Tolkien
Album: The Hobbit
Album Artist: J.R.R. Tolkien - Hobbit
And so on.
In the Finder this will then be the result:
/iTunes Media/Audiobooks/J.R.R. Tolkien - Hobbit/[Hobbit files]
/iTunes Media/Audiobooks/J.R.R. Tolkien - Lord of the Rings 1: Fellowship/[LOTR1 files]
/iTunes Media/Audiobooks/J.R.R. Tolkien - Lord of the Rings 2: Two Towers/[LOTR2 files]
/iTunes Media/Audiobooks/J.R.R. Tolkien - Lord of the Rings 3: Return King/[LOTR3 files]
/iTunes Media/Audiobooks/J.R.R. Tolkien - Silmarillion/[Silmarillion files]
And of course the author name can be Last-First in the Album Artist tag if you want the folders to show in proper Library order.
Depending on preference, in List View for Audiobooks, show column browser and control-click on the Authors heading then select “Use Album Artists”.
So it’s a workaround, it works decently, it’s relatively easy, and frankly I hate it. YMMV