This is backwards thinking. The dungeons are not copy pastes of outdoor areas, Siege and Freehold aside, they are dungeons who are designed as dungeons and then implemented into the outdoor world as an area for the sake of immersion since they're intended to be an actual space. If you're going to go that route, even ignoring the multi-wing part, the Auchendoun, SSC and TK dungeons are just copy pastes of their respective outdoor components/ associated raids.
You'd have a pretty hard time convincing me that more work went into throwing existing ethereal assets into mana tombs than went into Siege of Boralus. Even entirely utilizing an existing space, the parts that are modified for the dungeon specifically are higher effort and more unique than the entirety of those wing dungeon sets.