It would work if you pillar up more than 128 blocks above the ground so all mobs outside the mob farm despawn. Which you would want to do with a normal sized mob farm as well unless you've lit up all the caves within 128 blocks. (That's your position, the mob farm could be lower as long as it's close enough to you.)
It would be slower than a big mob farm but if it's the only place mobs can spawn then they will spawn there.
That's assuming you're in single player or alone on a server.
i usually make a dungeon farm of some sort that relies on a dungeon mob spawner. Creating a mob arm requires too much space, time and also often wont work (or wont work as efficient as it could) if you dont light up all the dark places around it (such as caves and holes etc)
Rollback Post to RevisionRollBack
I don't like giving too much info about the seeds i share. I feel like its better to let others explore and find out the chest contents,dungeon places and biomes. If someone is giving me a gift i would rather not know what it is until i open it for my self.