and Tom didn't dig deep enough to reveal Barzini connection
My thinking is that there probably was no Barzini connection at that point. I think Sol and the Tattaglias would have turned to Barzini first, and that Barzini told them that the Corleones would have to be on board. That sets up the necessity of the meeting, with the inevitable rejection from Vito and response from Sol and the Tattaglias.
Pete, I can see that reasoning. The drug traffic, as evidenced by Vito's and the Detroit Don's statements about drugs, was already up and running. Sol's drug operation was just one of what was probably several at the time. I don't see Vito's participation in it as critical, but only useful or helpful to Sollozzo, and the Tattaglia's. Barzini's involvement could have been from the outset, but probably emerged as Barzini saw it as a way to replace Vito as NY's crime czar.
By the way, a Consigliere doesn't drop from Heaven with consummate knowledge of the criminal underworld's machinations. Tom has his failings, but he operated in a much different, fast-paced environment than did Genco. Also, neither the novel or the film give us all that much information about Genco's successes and failures.
