If this is Aus at its worst then fuck me you lot have nothing to worry about. When Ireland, England, France or Wales hit bad form we often drift outside the top eight, sometimes slipping to ninth or bloody tenth (for perspective, where Japan have been occupying the past weeks).
Narrow defeats to Ireland and England teams playing better than they have done in the past ten years isn't the end of the world. The only issue is if Cheika can fix the defence before the RWC with only 5 matches left. But to be honest, the guy is coaching the Tahs so he can test out a helluva lot of stuff with players that will be in your RWC squad regardless. You're basically getting extra training there.
The ARU should be trying to pencil in one or two more training camps. Unlike in England or France the franchises are under direct control of the union, more camps more cohesion. Personally it does look like the team will fall just short of their potential at the RWC, but who knows, you only need form for just over a month, play like you did against Ireland and England in the first half and they'll be there or just about.