I hear the striker's flash bang grenade is great for hordes as well as Fist Of Havoc being great as a panic button. Maybe have a Titan or two with this? And stick together. Do that too. If someone dies, leave them. Especially if you're close to the bridge. Remember: Only one person has to make it over the bridge (Hunters are faster). Warlocks do great damage with both classes, but Voidwalker is the one to go with to clear huge thrall hordes.