Make Dungeon Spawners Larger

Whenever we find a dungeon spawner that we want to transform into a farm, we have to almost completely destroy the dungeon itself in order to maximise the spawnable area around the spawner. So why not just change the dimensions of these dungeons as they generate naturally? I think the ceiling should be three blocks above the spawner, the floor four blocks below the spawner, and the walls four blocks away from the spawner. Maybe just have the spawner generate on top of a four-block-tall mossy cobblestone pillar, and connected to the ceiling with three blocks of mossy cobblestone on top of it, so that mobs don't generate on it. This would save us so much boring excavation and destruction of the dungeon. And actually make the prospect of creating a dungeon farm more appealing and less tedious.