Langer?
Anyway I'd dispute that Hayden, Ponting, Martyn, Clarke, Katich and Gilchrist underperformed - they were just worked-out (Hayden, Clarke, Gilchrist) or stripped down from sensational to good (Ponting) or good to poor (Martyn). The only Aussie who really underperformed badly in 2005 for my money was Gillespie, and it was crucial. And truth be told the only time McGrath bowled well in the series was the opening afternoon - though that spell where he knocked-over Trescothick, Strauss, Vaughan, Bell and Flintoff in about 6 overs was as sensational a spell as you'll see as long as you live.
Langer underperformed by his standards.
Interesting you say that Hayden was worked out. He was coming off a good twelve months of bad form in test matches at the time, which would have been career ending if it was not for the hundred in the final test.
Martyn was the unlucky player of the series. He'd just had a huge year in international cricket and was dropped on the back of the Ashes alone, even though he'd been sawn off on no less than two occasions (really bad decisions too).
Clarke was a relatively new player at that stage, and had some technical weaknesses in his game which were exploited by more than England - remember he was dropped a series or two later.
It was a series in which so many factors combined to give such a memorable and enjoyable series of cricket - underperforming Australian stars, a huge sense of belief among the English team, career best performances from Flintoff, Simon Jones and Hoggard, some really horrible umpiring, wickets from no balls, sugary mints and misplaced cricket balls.
Remembering back, when McGrath slipped on the ball before Edgebaston everyone thought that he'd be out for months. It really was a miracle that he was fit to play by the third test (though he had an elbow problem in the forth). There's no way he was near full fitness for the two tests he did play in after the accident. But even with his injury he was clearly the second best performing Australian bowler.
Lee, Kasper and Dizzy were all attrocious, which was really surprising as Lee was looking white hot in other forms of the game (and heck, he was even looking good for some of the Ashes), Kasper had been in great form and Dizzy had been a champion up until then. It's a real shame that Dizzy will be most remembered for his woeful Ashes and then his 201* against Bangladesh. A bowler who takes over 250 wickets at 26 really deserves a better sendoff than what he got.
There is no way that Australia were functioning well as individuals or a team, with the exception of Warne and McGrath. Langer was ok (but nowhere near his best) as was Ponting, but the rest drastically underperformed, while England overacheived. And in the end we had a series that was decided on the last day of the last test.
I have to remember to buy my copy of the dvd.