Hope I’m right here with this, sorry if the question is too specific for this community.
I think the community is small enough to not get split between 4 sub communities. I don't play D&D but can't help much ?
Have you tried to evolve toward a more ? Strategic management game ? I assume that at this level they aren't anymore the one crawling dungeon but the one hiring NPC to to do. That they own a whole continent if not a whole plane, and even though they could use the nuclear option the political/diplomatic consequences might be to big. (think about real world, and how nuclear power still loose conventional war because of the political price of launching a bunch of nuke and turn a hostile country into a radioactive wasteland) Now is it what your PC want to do ? That's another issue