The novel says that the general view of Michael was that he wasn't the man his father was. Even Tessio and Clemenza, while giving Michael credit for a "bravura performance with the Turk and McCluskey," thought he "lacked force." Of course, that's exactly what Michael wanted: for both friends and enemies to underestimate him, the better to test loyalties and expose weaknesses. After the Great Massacre of 1955, the survivors had a different view of him.