P.S. I do not play with vassal states; to each his own.
In any case, isn't the case that creating a bunch of vassal states is inconsistent with trying for a domination victory?
(It would be consistent with other types of victories.)
Just noticed this comment. I've purposely balanced dissent with the expectation that players will need to have some colonies/vassals in order to achieve Domination victory. Otherwise, what is the point of having such mechanic if the best strategy is to ignore it? 50% of the land and population of a vassal counts towards its master's progress, but a vassal's dissent has no effect on its master. Nor are vassal cities counted when the master's civic dissent is calculated.