I hear Holy-Nightmare say this a lot, and I agree. There should be a method to manage aggro. So here's my idea,
Each enemy comes with an invisible meter. This meter can go from 0-50. When the meter is on 0, the first knight the monster sees will cause the meter to go up by 5 and the monster will chase after the knight the monster spotted.
Each weapon has a built in value that increases thr aggro meter by a set amount. The monster will chase after the knight that stacked the highest number.