I agree 100% with all 4 of DT's points.

Sonny would have found Fredo's sexual proclivities hysterical. He might have tossed a bridesmaid and a couple of cocktail waitresses together, himself.

I also think that had they gotten through the five family war, Sonny and Tom would have eventually been a very formidable tandem as boss and consigliere. They really cared deeply for one another.

I think if Moe Green's slapping Fredo around while Sonny's alive, he gets away with it once, because he was a cash cow for the Corleones, but never again.

Then again, Moe didn't respect Michael, that's why he didn't have any reservations about hitting Fredo in the first place. If Sonny was alive, and the Don was at full strength, Moe probably keeps his hands to himself.

Sonny's passion allowed him to be compassionate. He couldn't have killed his own brother. Again, Fredo wouldn't have resented his older brother anyway, so it would never have happened.

Michael was a survivor, no doubt, but his biggest flaw as a boss was that he was deeply flawed as a human being.