Well, I took a look at this one, for example:
https://standardebooks.org/ebooks/jo...re-and-conduct
It has
<dc:creator id="author">John Dewey</dc:creator>
So shouldn't 'copy' use that to fill in the author_sort?
On the other hand I see an extra property, perhaps Calibre is using this value to populate author_sort:
<meta property="file-as" refines="#author">Dewey, John</meta>