The super hornets where ordered as a stop gap due to the JSF delays and are obsolete in the near future as they are close to/if not already outgunned by the SU-30+ aircraft in the region.
Says who? Airpower Australia? Air combat power is more than simply the jet at your disposal. I'd be willing to put money on the fact that Australian Shornets working in combination with Wedgetail, Growler and our tankers would defeat almost all Russian based threats in the region very easily.