This quest is marked as a level 48 solo quest. It should not be. The amount of mobs around the gate can vary from 5-11 depending on how many are walking by and how many nearby mobs are chained to those. It is almost impossible to kill them all before the ones you first killed respawn again. However with the help of one other it becomes easy. One person can get agro and kite them around while the other person opens the gate, completing the quest for both.
It is not obvious the first time you do the quest but you do not right click on the gate or the counterweight hanging above the gate to open it (though you would think so since the counterweight is glowing blue as if it is a quest objective.) What you do is to attack the gate smashing it. In light of that, another strategy might be to go into defensinve stance and just stand there smashing the gate with 9 mobs on you. If you can do it before you are beaten down then just run away, if you aren't cornered in by the mass of them, or die and revive with it completed.