Haven’t watched the Godfather trilogy in a long time. It was clear, though, that Michael had regretted his decision, seeking redemption through philanthropy, revitalizing his relationship with his family, and papal favors (albeit beneficial to himself). His brothers were gone, and he was left with a vast estate, but filled with eternal loneliness, until death, yet not quite. Fredo was kept around until he wasn’t needed.
Although Michael’s narcissism was on full display, reaching the level of psychopathy, Fredo is an overlooked character in terms of ruthlessness. Yes, his one shot at being a big player failed miserably, almost costing more than Michael’s life (something to consider when evaluating the TS’s question), but he was a slippery character who wanted to be a criminal from the beginning, moving against the family and trying various criminal schemes along the way. He played Michael until things fell apart, conspiring with established and not-so-established players, then, when the dust settled, claimed to be naive of what was happening. It was part authentic, mostly manipulation, when he acted as though he had no idea a hit on Michael was in play.
Edit:
Fredo was essentially exiled, prevented from engaging in family business on any serious level. Once his mom was gone — donzo. Michael had to finally make the difficult decision while considering some of the aforementioned information above. Would I have done the same? Yes. Fredo almost got K killed, too. He was so far off the reservation that no redemption would be possible, not in that life. Moreover, Fredo was essentially given an out, at least in my view (again, haven’t rewatched in a long time); he had people looking for him in all the right places, but couldn’t stay away.
