I don't think Afridi was defensive at all. You also have to look at Pakistan's batting. We didn't use to have any proper batsman, just bits and pieces players, so he had to keep the batting deep. Specially as our bowling is already our strength. We won each world cup match because of our bowling, who were able to restrict the other teams to under par scores. And we only lost because our batsman could not even catch (NZ and India matches).
So having deep batting was important, specially because we had very aggressive players in our openers (Hafeez, Shehzad and Kamran Akmal) then Afridi, Umar Akmal and Razzaq lower down. And all of them apart from Misbah and Asad Shafiq are naturally aggressive players. And usually with agressive players is that they will fail often, but when they go on they will win it on their own.