I don't see any way for a 2-1-1 vote being effective because it essentially assumes that the two single votes would never talk with each other. Let's say you have an alliance of three versus a solo opponent. If that solo opponent wins immunity, then obviously the three-person alliance has to turn on one another. The immunity winner has the power because obviously, whoever they vote for is in a lot of danger. A tight three-person alliance would obviously find out who the outsider was voting for and vote that way to protec the other two. If one pair is tighter with each other than with their third ally, then obviously that ally will feel unsafe and vote with the immunity winner. A 2-1-1 vote basically requires players too stupid to talk to each other and too blind to realize the closeness of the twosome.