Benefited in WPM from stronger batting outfit and less draws per era.Fair point but Steyn still has the highest WPM remarkably. Pollock was in the twilight of his career, Kallis only bowled 20 overs per match. Morkel and Ntini were decent (Morkel has the fewest 5-fers for anyone with 300 wickets, I think).
I think Steyn also benefited from a solid batting line-up the most too.
Lost out in WPM from the speed his teammates were striking at- guys like Morkel and ntini were not great bowlers, but they were great strike bowlers.