The problem with them was that they had a stint at low loyalty a while back before we had loyalty trackers, and that makes us somewhat distrustful of their culture. Admittedly, I'm not sure how relevant it is at this point, since that was a long time ago.For the most part, it looked to me like they had natural, healthy differences for a march. Ancestral Honor is bad in the main hierarchy of the system, because it increases a lot of the stratification of the elite (and the upside isn't huge for them.) But it's actually quite sensible in a march. You need heroic generals to hold the line against your foes, and you're sufficiently isolated from the reins of power that your stratification matters less.
Another note. The Stallions now have a major cultural nexus in the Dragon Graveyard, so they aren't just a march. They are what is rapidly emerging as the second pillar of our religo-cultural axis, and therefore subject to greater scrutiny then e.g. the Heaven Hawks or something.