Using the Schwartzian Transform is very efficient when you want to do something with which element, and sort it by the result. In that case, generating a new list with items and their generated sorting "keys", lets you process each item only once, instead of many times.
But, in this case, you sort by an element of a hash, and the sort in the Schwartzian Transform must sort by an element of an array, so there's no gain. Actually, you lose, both time and simplicity.