When i say muscle I mean they were pawns in his plan he used them because of their feud with Pantangeli. The rosato's were important in his plan because of their feud with Frank and he wanted to get Frank to turn informant
I suppose I can see where your coming from. When Micheal realised that Roth was the one who tried to have him killed, he should maybe have had the Rosato's dealt with, knowing that Roth may use them against him.
However, as noted above, he did have reasons for not dealing with the Rosato's, so he could preserve his relationship with Roth and then find out who the traitor in his family was.
