I think that Vito was much more perceptive than Michael, as well as honestly interested in, the ups and downs of people's daily existence. Michael couldn't care less if you were having problems with a landlord, or needed a small loan or wanted to stop by for coffee and chat.

So Vito would have picked up on a brother's disenchantment much earlier and have arranged for that brother to be kept very close and have given that brother seemingly what he wanted without giving him any real power or authority.

In Fredo's case his resentment came from the fact that he was older. He wouldn't have had the same problem with Sonny. And maybe not even with Tom.

A Vito in the same position would have publicly declared his brother his counselor and let everyone know he didn't make a move without listening to his brother. He would have made sure his brother was listened to and extremely well paid..even if Vito had other "real" counselors or only really allowed his brother to make decisions or give advice on things that either didn't interest Vito or were of no importance. Vito would have kept in contact with his brother and never acted "high handed" or allowed others to give the impression that he was "high-handed".

Michael lacks that personal touch, which is why, among other reasons, his relationships with Kay, Tom, Connie, and Fredo became so tense.

That said, once Fredo's plotting or mistake , led to the almost deaths of Michael and Kay, I'm not sure that any mob boss could have forgiven that.