Afghanistan is one of the most, if not the most hostile of aviation environments on the planet - fact. Puma 1 would have been able to carry a fraction of the 16/12/10/whatever troop capacity in high summer and therefore not be an asset to Op HERRICK and hence highly vulnerable to getting cut completely.
Puma 2 may still struggle to bulk out before it hits MAUW in Afghanistan but nevertheless should still get close to max-capacity on most occasions. As such that represents a useful asset. It may not be the gold-plated Rolls Royce solution but it still counts as a capability upgrade in my books, if not exactly the best value for money.