Exactly. How would McGrath have reacted to a batsman leaving every ball? The same way he did after NZ tried the tactic against him which is the same way he reacted to any batsmen trying a half-arsed tactic against him; bowl better. It's a myth that McGrath bowled out-side off-stump, moving it away every ball and that was his only trick. In fact, early in his career, his only really effective ball was his in-cutter, which was a brilliant ball. It's actually quite funny to hear him considered a one-trick pony for moving the ball away when before the late 90's, he was considered a one-trick pony for moving the ball in! Once he developed further tricks like the away-cutter, out-swinger, etc., that was when he started to consistently trouble opposition batting line-ups.
As for McGrath getting wickets because batsmen go after him more, that's another myth. You just have to watch any random highlights package and see how many batsmen he pinned on the crease, clean-bowled or had caught behind on the defense to know how crap that is. But aside from those, McGrath got his fair share of wickets with the 'pin the batsman on the crease then throw him the wide one' but no more than anyone else.