There's a fundamental problem here which is the assumption that Darth Vader's repentance was genuine, good repentance. I'm not convinced of that. He acted based on his emotional impulses to protect the life of his own kin. He hasn't improved. He's still putting his personal desires over all. It is just that his personal desires in this case happened to coincide with doing a good action. There's no evidence that Vader has an ounce of sorrow about killing millions of people or any real remorse for the truly horrible actions.
I would have forgiven him pre phantom menace. Annoying Anakin Skywalker, AKA, new darth vader deserves death.