The seniority argument is so short sighted and perpetuated by those that benefit from it. It is probably the single biggest barrier to improved conditions in this country.
I do concede, however, that it is probably necessary because Australian pilots demonstrate time and time again that they will screw their colleagues for their own benefit, or their sons, or brothers etc. Hence seniority is the worst possible system, except for all the others.
Edit: The counter to the drawbacks of seniority is a strong unionised workforce that ensures Companies can't take advantage of the inherent stability that seniority provides management. Anyone seen a strong unionised workforce around here lately??