LW, I think you missed a few things. For one, Michael introduces him not as his brother, but as Tom Hagen. He could have easily said "My brother Ton Hagen." In huge contrast, he introduces Fredo as his brother:"my brother Fredo"; and Sonny: "when my brother Sonny was a kid, he found Tom Hagen in the street." Not Tom, but Tom Hagen and, again "my brother".

Then later: "He's a good lawyer. Not a Sicilian, but -- I think he's gonna be consiglieri." That's hardly an endorsement.