There is no way that any Australian operator would see the 457 Visa as a way to get experienced and qualified crew at lower wages than paying qualified Australians appropriately.
And similarly, no experienced pilot in their right mind would come to Australia willing to accept work on 457 Visa at wages lower than a qualified Australian would/could accept. Oh, hang on, did you say that after 5 years on a 457 at crap wages I get Australian citizenship? Gee, let me think....
These things just wouldnt happen in Australia.....