There seems to be some problem with the drow proving grounds quest in that not all classes are rewarded at its completion. Marathon had a problem with a paladin/CoT and I had a problem with a pure druid. Also my ranger(12)/wizard(1)/arcane archer(27) got an item for a wizard
I suspect that the reward script looks for a character class that it recognizes and dishes out an appropriate item. The conversation finished after my druid spoke the line "The battles were very hard, but I defeated them all. What reward do I receive?" and I was left standing there rewardless.
Classes that I have received rewards for are bard, cleric, monk, rogue and wizard. The cleric item is very good but shouldn't it be heavy armour?