I was thinking along the same lines, though not as coherently. Everyone, except for Will, was self-serving in the film. I knew that they filmed 2 & 3 at the same time, so the sudden ending wasn't too jolting, as I knew 3 was already in the bag and thus making it one long story.

From that perspective, that 2 & 3 are one long plot, the storytelling would be "characters all brought to their lowest points before they're built back up to their most heroic." I agree that Norrington better have his own redemption, too, or else it would be a waste of character.