[Apart from the fact they're set fifteen years after the main story you are absolutely right. And you didn't play as Edward in AC3, you played as his son Haythem. So apart from being wrong about everything you're absolutely right
Lol, totally fluffed that up
...but you knew what I meant which is the important thing - could easily have been part of the main game as some sort of flash-forward / flash-back thing.
Don't get me wrong - I don't mind buying extra content, I just don't like the idea of paying for something that maybe should have been included in my original game purchase.