[@WilsonTurner]Your very first error here that you assume everyone in the Dominion is evil.  Pretty far from the truth. Majority became theDominion's vassals because that was either beneficial to the or they had no choice. These factions have little if any need against the FPA,  they assist the Promethean because that's written as their obligation within their "contract". That and in spite of the Prometheans arrogance and , they have a solid system. Most civilizations under them may even live better than before.  So a somewhat mutual gain based system combined with the fear of the Prometheans power are already ensuring the Dominion is stable.  Of course there are factions with their own agendas but you'd be just a few droplets in a big pond. Other manipulative and ambitious factions may even ridicule you for this. The Dominion is already a convenient system for you.  A manipulative nation can get far more by using "peaceful"  methods.  Worming your way into the Promwtheans' best graces.

Your idea is naive because you assume the vassals would uniformly rebel against a system most of them likes or at worst neutral about. Ironically you can be called naive because you think every single vassal is ambitious,  scheming and evil. Your idea that the Dominion would crumble by internal wars goes under the assumption allof  them are like you. That's .a fairly .common error to do,  actually.