When Michael said "Tessio was always smarter" was that Tessio was able to recognize change quicker than Clemenza. Clemenza was a drunk. It was he that allowed that little greedy runt Paulie to call in sick giving the Tattaglias the opening they needed to shoot at V Corleone. Clemenza had a heart, meaning he believed Hitler should have been stopped before 1939 but he was not able to see that people were looking to kill Vito in order to bring in their narcotics (opium/heroin) supplied to numb the pain associated with death. Vito sent Luca to the Tattaglias because Luca was dispensable. If you read the novel Luca Brazi was a stone cold sociopathic killer who was suicidal and didn't want his bad gene's to be passed down to a child which is why he had the "prostitute" killed for having his baby.


Tessio was honest, in the film he wanted to part ways with Vito but Godfather didn't want that. As far as Michael shooting Sollozzo I can't really comment on that because I, like Tom Hagan, feel that Sunny should have kept his cool and focused a little more on being productive and not so over eager to join forces with Sollozzo. Yes, Michael was very intelligent and he didn't seem surprised that Clemenza would follow order's till the end. Tessio was angry.. and I'm almost thinking the writer's threw in the "Tessio was always smarter line" because they already knew a second film was going to be released, which it did, around 1978. At that point Tessio must have thought that Carlo was going to be the right hand man which is why he approached Michael with the meeting because by then it was clear he didn't want Michael to be head of the family.