The key to making taunts effective is using early removal so the warlock is forced to eat through the taunt inefficiently. Relying on taunt/aoe is exactly what the zoolock wants you to do because the taunts/aoes people rely on are too high in mana to be used early.
Yeah, if you don't have any minions in play, you can't make value trades via battlecry buffs. You get mad value if your 3 attack minion eats through a 5-6 hp taunt while you continue to flood your board.