In the first draft of the script (the only draft availabe on the internet) the Russo Brothers are running the former Corleone businesses, but in turn they work for Don Altobello. Why would any boss of the most powerful family need to work for a boss of another family? It doesn't make sense. The only explanation is that the Corleone crime family has become weak and is therefore dominated by a rival family which has become more powerful. But then; how could Michael still have control over the Commission if he didn't have the muscle anymore?

I wish Puzo was still alive to explain. Why don't we get an Ouija board and try to communicate with him.