I think we have to rethink the idea of claiming completely. Due to larger amounts of open spaces in the Good lands, we should make something different, in order not to make it look absurd.
I suggest something like Influence areas. Similar to how Scourge in WarCraft III spreads. You get out of the underworld and begin corrupting the territory.
And form the hero side, some creatures would oppose the corruptors. Say, druids. These creatures would heal the land back. not tile-per-tile, but by small location at once.