Cornell is a baritone that could go way lower and higher with far more power. from a techinical standpoint you really can't fuck with the guy.
He's awesome. Though in terms of classical voice technique, Bruce Dickinson ranks even higher.
But rock singing has always been about more than technique. Projecting power and sex are at least as important. In that respect, Elvis is way, way up there. But I stand by Percy."I AM A GOLDEN GOD!"