If you look at the code in class-asp-search-indextable.php, there are variables and a str_replace for the {orderby} query placeholder that you have in all of the search helpers, but {orderby} is not actually included in the query (around lines 396-398). I don’t know what impact this has, but just thought I’d let you know.
Thank you for letting me know. It is intentional, because it does not apply for the index table – the columns are not present for ordering, it is done via a post process function.