If you remember, Fredo had as much a hand in the Family Business as Santino and even Tom - Fredo was in the initial meeting at Genco with Sollozzo, along with the Caporegimes Clemenza and Tessio, Santino, Vito, and Tom. You didn't see Michael there.
Up until the time of Vito's shooting, Fredo was right there.
Yes, Fredo was in the Sollozzo meeting and Michael wasn't. But there's no evidence that Fredo "had as much a hand in the Family business as Santino or even Tom." If you remember, Fredo wasn't in the meeting that Vito had with Sonny and Tom re. Sollozzo after Tom came back from his meeting with Woltz. Nor was Fredo in any of the meetings that Vito had during Connie's wedding party.
