I do have to wonder if there was some personal element in Barzini's seemingly obsessive desire to destroy the Corleones? Yes, he'd become much more powerful with them out of the way. But at what cost? At what risk? The urgency of his actions, and the rapidity of it all, makes his actions seem almost personal rather than business. Barzini's moves were calculated but they were very rushed. Contrast that to the Corleone plan. The Corleone's wiping out of the rival Dons was much less subtle, but also much longer in the making, more thought out and ultimately more effective.

Barzini was taking on a lot of risks and making a lot of assumptions. That Sol would be an obedient puppet and not simply align himself solely with the Tattaglias. That Tattaglia would be willing to be the front-line combatant in what could be a long and devastating war with the Corleones. That Vito would let his guard slip. That Sonny would be a hothead.

He was playing a chess game, but he seemed to be rushing through it rather than taking his time and playing out the possible scenarios. Again contrast that with the Corleones - they took a calculated risk - made themselves purposely weaker - so that they'd be less expected to strike, and when they did, it made them that even more powerful than Barzini could've dreamed of being. Michael could easily install four other puppet Bosses, absorb the drug business, and win back all of the Corleone's lost business and territory.

Where Barzini's end game was to simply take Vito's place at the head of the table, Vito/Michael's was to not only head the table, but choose who sat at it as well.