No, of course not. That's not what I was suggesting at all. However, he also bowled straight balls at the stumps, which are not terribly difficult to keep out either.
Why did he go from bowling well on flatties to not to doing so again? I honestly can't begin to know. However, it's not a question of losing the skill to work batsmen over, not at all. I will maintain all my life that most of McGrath's wicket-taking spells between 2001/02 and 2004 were not the result of particularly good bowling. I'd only ever seen him bowl occasionally before then, mostly on seaming pitches, so I've no way of knowing much about the pre-2001 stuff.
I mean, let's just have a basic (this is very simplistic) look. There's 101 wickets (26 Tests) in
the period in question) so I really can't be going through all of them. 4 of these Tests (19 wickets) are irrelevant as they were pitches that helped seamers (those FTR are The WACA 2002/03, Darwin 2004, Nagpur 2004/05 and Mumbai 2004/05). So 22 games, 82 wickets.
We'll assume that the 15 tail-enders (Tufnell, Ormond, Nel, Shoaib Akhtar, Murali Kartik, Hoggard, Henderson, Donald, Dawson, Ntini, Waqar Younis x2 and Saqlain Mushtaq x2) don't really need working-over and are "easy" wickets, so that leaves us with 67 to look at. I don't have time to do them all now, and may never do. But I'll put those from The Oval 2001 here for starters as examples:
Usman Afzaal - caught fine-leg, very poor stroke
Mark Ramprakash - caught behind for 133, cutting at an innocuous delivery as he had to try and up the run-rate with wickets falling
Michael Atherton - caught slip, I seem to recall this being a decent ball as so often between these two
Marcus Trescothick - caught and bowled, ball that spat off the pitch (a freak on that pitch as it almost exclusively played beautifully), obviously no credit to the bowlerUsman Afzaal - caught slip, not a good ball at all, far too wide, driven erroneously