As a grad one's ability to attain the higher ranks is very difficult!
Is it not also still the case that "The Chosen Ones" are identified and fast-tracked at an early stage? To generate a CAS requires two tours max (one Op/Exec and one Staff) in each rank (one at 1*) otherwise there's insufficient time to climb the ladder, does it not? It was certainly easier when most sqns were populated with fg offs!