Why interpret what the novel and film doesn't say about Genco as a criticism of him? Neither the novel or the film was about Genco. If Puzo and FFC have the novel and film characters say good things about Genco, then who are we to dispute it. Fictional as those characters are, they were there, we weren't.

The novel tells us that Vito's naming an Irish (non-Sicilian) consigliere was one of Vito's few mistakes. I have no body of knowledge on which to base any disagreement about that. I know that I don't know what is a wartime consigliere. So, I have to defer to Michael's judgement about Tom.

"Generosity. That was my first mistake."
"Experience must be our only guide; reason may mislead us."
"Instagram is Twitter for people who can't read."