[Lukeatus]

You must use it on the right region. It helps because it creates havock by itself instead of you having to kill them all. However, the only trully easy way to complete this mission is with high celerity.
Animalism 5 really helps, but you still must hurry from 1 gate to the other, go to 1 gate, use pestilence, turn around, go to the other gate, than do the same. If you have the occult item I talked about, it really helps you as you have a nice blood supply to use on the run.
Dominate 5 is much easier to use, (everyone just suicides, even though there's a bug - dead zombies sometimes don't disappear - their bodies die but they stand still anyway, but they can't bash the gate) but animalism 5 is great if you place it right, a lot easier than hacking through them.