I totally agree with your points, dt.

On a number of occasions I've posted that we don't see anything in the films demonstrating Genco's acumen. Even in flashbacks, we don't see Vito look to him for advice.

The "Genco is brilliant" school of thought seems to rest heavily on Sonny's "Pop had Genco look what I got" insult to Tom and, in the novel, Tom's assertion that "Genco would have smelled a rat" after the hit on Sonny.

My theory is that Genco was really not consigliere in a broad, strategic sense. Vito really seems to keep his own counsel. I don't see him talking strategy with Genco.

I see Genco's role as someone absolutely trustworthy who could get Vito information. As a shopkeeper's son, he probably knew the neighborhood very well. He could tell Vito what was brewing and give his impressions of the people involved.

As Vito's empire grew, Genco grew with it.