They could have ruined McCluskey but then Sollozzo just gets another high profile bodyguard. Waiting to disclose the info was the smart move because you want Sollozzo to feel safe when you get to him.
The mafia is all about power, violence, and money. I think going right after the Tataglias and Sollozzo was the right thing to do. You go to war by attrition and you win then your enemies are devastated and you can build up stronger than ever.
My question is: Barzini and the Tataglias would have needed commission approval to hit Vito. The fact that the other families don't join in against Sollozzo and the Tataglias seems to point to the fact that they did have commission approval for the hit.