What if kingdom size was restricted to 5% of the server size?
Generally a server has most players at the start, so say 2000 people started then max for one kingdom would be 100 members
then as the server progresses we usually see a drop in numbers, typical number for endgame is now 1000 so then 50 players per kingdom would be max they could have.
no one would be kicked if they still had 100 members, they just wouldn't be able to recruit more until they had less than 50 (aka 5%)
so it would mean those teams wanting wings would have no way to merge them all into one place for the endgame, making it less optimal to plan for this happening later in the game. Thus hopefully meaning newer, less experinced kingdoms could stay more viable throughout