The Luca backstory is really interesting. I think if the movie were remade today it might include some of that. The thing is that Luca is scarier/more of a cipher in the movie because we don't know much about him and that if we did know more about him it would have reduced sympathy for/identification with the Corleones. Luca is after all an abuser/murderer of women and children.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.