You can try with the following query, where the author data as well as the post count can be retrieved.
$sql = "SELECT SQL_CALC_FOUND_ROWS wp_users.ID,post_count FROM wp_users RIGHT JOIN (SELECT post_author, COUNT(*) as post_count FROM wp_posts WHERE ( ( post_type="custom-post-type" AND ( post_status="publish" ) ) ) GROUP BY post_author) p ON (wp_users.ID = p.post_author) WHERE 1=1 ORDER BY post_count DESC";
$result = $wpdb->get_results($sql,OBJECT);
print_r($result);