see i don't think anyone's saying anderson is an abjectly bad bowler, which, if that were the case sure i'd agree he is underrated.
the case is that while he has had some good overseas performances (such as, as mentioned by
@GIMH before in the tour thread, when england came here and won and did the same to india too), but by and large he's failed to stand up and be counted and be
great overseas when the team's needed him; all too often in australia he's been middling, which, again, when you've got a pattern of doing it it is a black mark. you have to credit the guy for coming out every time and putting all the miles in to his legs that he has in crushing ashes defeats here, but as they say one swallow a summer does not make, and having the odd good overseas performance doesn't erase the rest of it.
again, that's not to say he's rubel hossain every time he comes to australia
just that by and large he hasn't been able to be great overseas - same criticism that is rightly levelled at dave warner (though jimmy's a better overseas bowler than warner is an overseas bat); and if you can't deliver that as the leader of an english attack you deserve the black mark, just as would australians who can't deliver in away ashes on the isles.