You are partially right and partially wrongE-3 is not a dual intent visa so you need to show you intent to VO. To return back to Australia upon you job completion.
One needs to be in H1 or L1 to apply for GC otherwise in other categories it can be rejected under 245b
Although INA § 101(a)(15)(E) requires that all E nonimmigrants maintain an intention to depart the United States upon expiration of their authorized E stay, the guidelines issued by the USCIS state that applications for E classification, including extensions or change of status, cannot be denied solely on the basis of an approved permanent labor certification or pending or approved immigrant visa petition. Therefore, immigrant intent should not be a bar to eligibility for E-3 classification.