Thats a touch disingenuous. It was never meant to power the whole of South Australia. It was specifically built to mitigate the peak power price gouging [0] that had been happening the for prior 10 years.
The 6 minutes it can run for during each cycle saves millions of dollars a year. Specifically 40mil in the first year. The cost of the unit was 66 Mil [1], so thats an insane break even time for grid infrastructure.