If I put all of my realm into the same duchy, and then create a second one-region duchy out of a dinky townsland, and organize myself for a badland to join the dinky duchy and for the townsland to then join the main one, and then switch that duchy to another realm, effectively moving all regions except for the badland. Would this not be a realm merger?
a) You can't do that, because the game requires at least one city or stronghold to remain with the realm.
b) Do you not get the difference between stealing the main duchy out from underneath its outraged ruler and deliberately planning the total merger of two realms?