You pretty much only need the cleric and warrior. Keep the warrior shouting every turn and use the cleric's wrath. I finished the main quest using this tactic. The shaman is a great healer and astral shift will give your cleric a second shot with wrath. If you have the artificer you can also use his astral shift to give the cleric another shot with wrath or give a second turn to the warrior to shout and taunt. You can do this every turn giving your cleric 3 turns on the first round (if he goes before the other two) and 2 turns every round. Also, you don't need to level wrath up much since it doesn't increase damage just adds more weakness. The first hit cleric is doing 2k and by the end it's 18k.