I didn't mean that as a criticism. Those were just my thoughts as I read the book. I lack deep knowledge on the subject, and I'll leave meaningful debate to the experts. However, if "Meditations" were the root source of stoicism, I think I'd take issue with it as described here alone.

I do disagree with your specific reasoning, though. Humans have an enormous capacity for adapting to horrid conditions by convincing themselves that it's not that bad. That's true in big society-level situations, and small personal ones: "Cut off my arm? I can survive with just one!" "This cancer isn't going to beat me!" "One day we'll rise up!" I'm not talking about Epictetus specifically. It's likely you know more about him than I do. I'm certain his condition as a slave was far different than that of a stolen African person in the Civil War-era American south, or people today in current places around the world. However, in general, I don't think "Epictetus is a former slave" is by itself strong evidence that his philosophy didn't allow for resignation to slavery.