The wetlands (TOUCHE, sir!) are not the same situation as Seanchan before the Empire. Those lands were chaotic and unstable, and the people had no concepts of honor and justice. The Imperials brought and imposed all of that and they did it by force because they had to. They are not the typical national government as we think of it, rather they are a long-term occupation authority or colonization force out of contact with home. As we see in the books (read the damn things, please), in lands they conquer which DO have a viable society and government, they leave it in place for the most part. That over-centralized system (from discussions on the CMB, it would be hard to imagine you needing to lecture me on the danger of an overly centralized government) does not seem to be the case in their Empire in these lands, since Taraboners et al, are more reliable than native Seanchan. You can leave a guy like Beslan in charge of Altara while getting on with the big stuff, but in Seanchan, the Imperials had to keep it all tied to the authority of the Crystal Throne, because all the locals were d-bags. They appear to be setting up a more federated system in the wetlands which is capable of surviving such a coup de grace as the mass murder of the Imperial family (though such a blow might destabilize the overall union, the individual parts would have their own identity and societal structures that would allow them to carry on - if Seanchan fails, the memory of Altara and Tarabon can stave off chaos).