You are not wrong! Capri the best option for Fredo, in hind sight, make a deal with Greene and let Fredo continue banging cocktail waitresses two at a time!

Whilst Vito could have guided, mentored, nurtured and embraced Fredo, Fredo still would have been a bad Don not dissimilar to Sonny for different reasons, nothing but the Donship would have sufficed for Fredo as we saw during Fredo's boathouse outburst

Perhaps some sort of consigliere role - an elder statesman - under the watchful eye of Tom....