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.
Well, Gale was such a prodigy he had sex with Mystra, the goddess of magic and after she ignored him he found a Netherese artifact left over from Karsus' Folly, the only 12th level spell ever cast where Karsus took over her body, the weave undid itself, she committed suicide, and a new goddess was born to take over and repair it. Gale then had this shadow weave chaotic magic from the time of days of the most powerful spells cast and items created and it somehow consumed him when he opened it and now has to feed it powerful artifacts or he thinks that his explosion would wipe out the largest city on the Sword Cost, Waterdeep.
