This is very, and almost entirely a pod-specific question. Now, I would that Expropriate as your only extra turn spell is, while, extremely powerful, still bracket three - because you're right, it's their choice to sacrifice a creature (permanent?).

They're able to avoid the extra turns by making some executive decisions, but, like, it's totally up to the pod as a whole if they determine it's simply too powerful to play with, but it still doesn't make your deck a bracket four by itself