Sorry, my man, it just doesn't add up. If they can create brains with their labs, they don't need us. Period. You say the labs are too busy, but they can just build more labs so they can divert extra capacity to brains (though I bet you're going to come up with some unlikely excuse why they can't). And the idea that they can't lock up a few billion humans is madness. I'll buy that thay would need to use a whole planet as the jail, but they would never, ever leave the prisoners alone without guards to prevent them from rising up in revolt.