Excellent analysis, JC. Thanks for posting it.
I agree that Barzini was brilliant in using Sol and Tatt as his proxies in his quest to become Numero Uno. I posted a while back that Sol, knowing Barzini's ambitions, probably approached him first, thinking he'd have the most to gain from an alliance. I never cease to wonder why Vito said, after the Commission meeting, "Until this day I never knew that it was Barzini all along...Tattaglia is a pimp--alone he could never have outfought Santino." If that was true, then why didn't you figure it out sooner? Duhh, Vito.

But Barz screwed up big time in the last plot. It was all so obvious: provoking the Corleones by horning in on their territory, then calling for a sit-down. Using Tessio, who was so plainly disgruntled in the fish tank scene, and so obviously servile to Barzini at Vito's burial. Barzini was getting complacent--just as Vito was before he was shot.

Roth was by far the most formidable enemy--endlessly resourceful and determined, with backup plans for each contingency. I don't agree that his speech about Moe was a big mistake--Michael already knew Roth was the Tahoe culprit and also knew his plan to have him whacked after the Presidential party.

You were insightful to note that Roth did permanent damage to Michael even though he lost the contest. In addition to what you said: Even though Pentangeli recanted his affidavit at the Senate hearing, Michael was subjected to accusations and revelations that, although not proven in a court of law, exposed him to millions of people as a possible Mob boss. People seldom believe that you're innocent until proven guilty. It was a blow to his legitimacy and self esteem.