I like the flashbacks (with Robert De Niro as young Vito Corleone) in Godfather 2, but agree that the first is better in a number of respects. I recall reading not long ago that apparently there was disagreement between Mario Puzo and Francis Coppola over Fredo’s fate in 2 as Puzo argued that in real life, Fredo would have been seen as a weak person on his own and therefore really not posing a threat to Michael. Thus, there was really no reason to have him killed but Coppola insisted otherwise. This is the aspect of Godfather 2 that I am not a fan of.
While Puzo would be right, Michael was big into killing all his enemies. No matter what. Hyman Roth was dying, Michael didn’t care, he had to KILL Roth, even if it cost him one of his best soldiers. And Fredo. That’s Michael’s arc, from “we’ll be fully legitimate in 5 years” to ice cold killer even willing to assassinate his brother.
I agree with Coppola’s logic.
Fredo may have been weak and stupid—but he managed to cause a lot of damage.
Fredo knew too much and talked too much—there was no safe way to keep him around.
If there were a future major law enforcement effort against the family Fredo would have been an obvious weak leak (as just one example).