Yeah Pentangelli was right.

I think at the specific times when Micheal told Frank to 'settle your differences with the Rosato's' it was the right decision.

Obviously considering what Roth was upto, you can look back on the decision and question it but I'm still not sure how removing the Rosato's would have helped the Corleones. They played quite a insignificant part in Roth's scheme in my opinion.