Because that group was full of scrubs. I have a level 30 warlock and hunter with over 30 hard raid completions between them and I can tell you with complete certainty that class makes 0 difference in the VoG. Golden gun for supplicants and oracles, Titan bubble for extra damage and Atheon platform safety net, Warlocks shouldn't use sunsinger because they lose damage potential of void walker and shouldn't be dying anyways. Each class has a valuable role in their, but at the end of the day the only things that matter are the level, the weapons, and most importantly, the skill of a player.