The companions have backstories, but I wouldn't call them "epic adventures." It's more like they screwed up their lives in various ways and got some powers on the side, but haven't done anything with it to make a mark in the world.
This is their first real adventure in D&D terms. The adventuring is what drives the leveling. I don't have a problem with it personally, but then I've played so many games like this that I don't mind hand-waving some of the setups. I'd rather be adventuring with this group than with a farm boy.
