Gee, Hauritz just can't seem to get a break. One good innings of bowling from North and people are already calling for Hauritz to be shifted out of the Test team?
It's a lot easier being a part time spinner because if you get carted around a bit or your economical but ineffective you get taken off after a few overs and it's easily forgotten. However, if you pick up a wicket or two the captain will generally keep you on and all of a sudden your figures look pretty good because the opposition batting line up throws their wickets away, like what happened to North.
I also think it has to be realised that Hauritz is a complementary bowler. He keeps the pressure on and allows the pacemen at the other end to attack and take the wickets as well as providing a balance for a pace attack that is sometimes wayward and not draw much movement from the ball and/or pitch.
Start bowling Smith or North as much as a specialist spinner over the course of several Test matches/a few Test series and I have my doubts that the bowling attack would perform as well in comparison to if Hauritz were part of the bowling attack.