from what I've heard the idea for this book came to him during the Brisingr days.

Interesting - where did you hear that?

And you're right; even if he did come up with the idea years ago that's no excuse for not having reworked it into something better and more original since then. I still occasionally refine and reuse the better parts of the stuff I came up with as a teenager, because now I have a much better perspective on what the more worthwhile aspects of them were and which parts need to be discarded.