However, having seen kids give up on the independent study route and beg to go to a standard school, I think you are underestimating how daunting it is to start learning high school subjects as independent studies. Fundamentally, arguing with your peers in history class or being able to ask questions in chemistry is really valuable. A video is interesting, but once you get to the point where there is a part you don't understand, it's really hard to make progress.
A lot of the "challenge" level courses seem to talk about class presentations? Is this a remote school more than homeschool?