I think the Dogs problem is in their forwards, not their backs. However other than signing Hetherington, the Dogs haven’t done anything about it.
Their pack is suited to the old style of the game, not the new faster game where forwards need to be quicker, have some footwork and ball playing skills and be able to play long minutes.
Their forwards simply don’t win the contest in the middle and rarely earn their side a fast play the ball or anything for the backs to work with.
Barrett seems to have focused on signing backs rather than fixing the forwards which is where he has gone wrong.