...DnD stories (or pretty much ALL game-based fictions ever) were never intended to follow the rules.
And if we're talking about kingdom-level stuffs? Story-wise curses are always the OP ones, but you don't see that doing much except for in Ravenloft, and those ones in there are mostly backgrounds.
Yeah, if you want Battlefield-level magic uses, go check out Warhammer TWG or most other army-level TWGs, not TRPGs.