Lanefan
Victoria Rules
The main reason to separate out the "heroic" (got to come up with a different term for that; not everyone's a hero) game from the legendary game is that there's so many rules and systems that work well at low level or high level yet fall apart when applied to the other.I thought about 3 boxes, but not everyone likes to play novice characters so I split it out. However, I would make them all optional. You could start with box 1 or box 3, it doesn't matter. Play the game you want to play. Also, I would make box 1 & 2 completely compatible, only differing in tone, with box 3 being the only one with features that are not always directly compatible.
I see no reason to have barriers between heroic and legendary characters. I do see there being some barriers to being godly characters.
So, split them out to avoid having to design rules that covers 2nd level and 17th level equally well.