Why do we even need S/O's in Australia? It seems to be a uniquely Australian thing (like most) that is useless around the rest of the world.
It's not uniquely Australian as it is in use with other airlines eg CX. What it does do, is lower the overall crew costs for long range flights in comparison with airlines that use 2 Captains & 2 F/O's. Some airlines use the title "Cruise F/O's" which is another name for essentially the same duties. Other cost savings are made in not having the same recency issues that Captains & F/O's have.