My two cents worth!
Vito and Michael, sentiments aside....
Times were changing
They were entirely different times, circumstances, people, nefarious or otherwise acts, Mafia family, blood family, wives etc.
Vito could have cut their losses and walked away from Mafia but he didn't because he wanted, needed the Corleone family reputation, standing, history etc. to be restored, leaving a murderous legacy for Michael
Vito planned all the baptism murders including making his daughter a widow for Michael to carry out after Vito's death
No doubt Vito helped people however with the stipulation “Some day and that day may never come, I'll call upon you to do a service for me”
The only exception I can think of was the help to Signora Colombo
Michael could not grant favours like Vito “must go to Don Corleone for justice” as he was supposedly a 'legitimate' businessman
Vito did not have the added burden of trying to make decades old Mafia business legitimate
Michael and Kay were unrealistic that such a feat could be accomplished let alone in five years
Did Vito pay attention to Fredo, his own blood son?
The way, at the garden scene, Vito dismissed Fredo and some!
"A man who doesn't spend time with his family can never be a true man" Did Vito?
If Vito did, I cannot recall other than business meetings Even with Carmela apart from Carlo and Connie's wedding photo
At the time of the brothers having drinks Fredo had said he had never met Roth or Ola
I believe Michael showed Fredo genuine affection