I’m surprised more people within the Corleone family didn’t have a problem with Michael jumping all of them to be named boss just because he was the son of Vito. Obviously the right choice was made but I can see why some people might’ve felt like Michael was just a spoiled kid who didn’t put in enough work and didn’t deserve to be boss. Tessio was handled, maybe everyone in the family fell in line after that.
No one would question Vito's choice, but the novel points out that many (in and out of the family) thought Michael put in "a bravura performance against the Turk and McCluskey," but he lacked "force." Tessio obviously carried that thought to the extreme when he betrayed Michael.
