Charm of the Subterranean vs relevant locations

There are not enough underground/bunker situations to justify Charm of Subterranean. Caves typically have 2-4 enemies, bunkers have around 3 Infestation POIs. There are only 1-2 bunkers per realm, and while there are typically several caves in forest/desert biomes they don't have many creatures to fight.

Increasing the charm's effect to cover vaults, including in Boss Rush, would make it more worth-while. There are many charms to choose from, and this is seriously lacking because it is highly specific to limited areas in standard realms.