Although whirl mode was catastrophic, you weren't going to enter whirl mode every time you went flying above a certain speed, otherwise it would have never got out of flight test. It was (like all accidents) a combination of factors. That combination never occurred in oz before the speed restrictions were introduced.
Had whirl mode not been understood following the US crashes it would have remained a hazard for the Australian (and other) Electras and eventually you may have seen one succumb to it.