This is an important point that a lot of people are overlooking. Unless I'm much mistaken, Perth was the first time that Australia had lost a Test at home under Lehmann. You have to go back to the last time South Africa toured in 2012 to find a team going to Australia and actually winning a Test, and you have to go back 5 years to Hobart for a side other than South Africa to do it.
Australia's batting clearly has problems but under Lehmann they still have a pretty decent away record. They've won series in West Indies, New Zealand and South Africa after all. I don't think they're the best side in the world but the way cricket is at the moment, they're not a million miles off it.
At the moment, the rankings say India and I'd probably go along with that. I think too many people here when they want to discuss who "the best" are want the number 1 team to achieve Australia/West Indies levels of dominance, and also expect the rankings to follow a simple "A > B > C > D > E > F > G > H > I" pattern. Truth is, Team A might be better than Team B, but in certain conditions Team B might be able to beat team F whereas A might not. Looking at football for a parallel, Arsenal took 6 points off Leicester in the league last season but that doesn't mean that Arsenal were the best team, because results against everyone, everywhere matters.