Do I understand you correctly and you mean a kingdom union should have 5 duke slots to cover more space on the map and that more governors can be within the kingdom border? Because so many governors are outside of the kingdom border? It's what I am currently facing in a game world I am playing on: I am constantly out of the kingdom border even though we do have a lot of wing kingdoms
Is so, wouldn't a fifth duke slot favor bigger kingdoms and metas again? Wouldn't it be better to have a separate kingdom in that area, even if it might be a so called wing kingdom. What would be more fun and a better player experience?
Wings are created because many good players can not be accommodated in 1 kingdom. And whats their goal then, its to work toward a union. If we have 3-4 duke slots before the union that will allow less wings. And if we have duke slots after Union then that will allow more fighting between different kingdoms at an early stage. Why? because more dukes means more territory to compete for.
Separate kingdoms which have less members dont act on their own much. If we have strong kingdoms which are bigger they may and as I see in travian legends where alliances work. Sometimes wings go on their own and even go against Main Alliances.