Perfectly said!
Part 1 is like the true story, and 2 - like it's continuation that might well happen, but might as well not.
Flashbacks seem to me insufficient, they don't contain the most important part of family history, about how he became really great. His wars with Maranzano, Capone, Irishers, and Luca Brasi's part in them, and Sonny's bones etc.
So I must admit I like the 1 p. just a little better.