I disagree with you to an extent their, he is in the team primarily as a spinner (well probably as an all-rounder) and the spinners job is to get wickets. Unfortunately he does not do that when he needs to these days.
He never has done... he's not that type of bowler given he doesn't turn it much, and we're never going to get a finger spinner coming out of NZ who is that type of bowler (nor from most other parts of the world) because of the decks.
How many ortho spinners who aren't freaks (ie: not Murali) can you name that do regularly run thru sides over the last twenty years?... maybe the Turbanator a few years back... one or two others but not consistently over several years by any stretch; and not compared to a wristy or Murali as you simply don't get the turning tracks as often these days because pitches are better and runs are scored quicker (making spinners potentially expensive) and hence why Dan has been as successful as he has - he can bowl long spells, be economical and usually picks up a wicket or two... on the odd occasion a few more.
The man, in our time and in our team has done brilliantly - as a spinner, and bowler. Who else would we have picked over the last 12-13 years instead of him?...