I think one of the issues with the vengeance fleets is that if they get destroyed by something that isn't you, they still escalate. I just checked my events, and the Hegemony Revenge description says that the Hegemony has escalated the conflict to the highest possible level, but I've never actually fought a Hegemony vengeance fleet. They almost always get distracted by something else, like pirates or a Tri-Tachyon vengeance fleet, and end up getting destroyed before I ever have to fight them… until they get so big they can just punch through everything in their way. From the players perspective, this looks like the angered faction is suddenly jumping to the maximum possible escalation level with very little, if any, warning.