Steven, Mary Beard is a bit too quick here. “Control” certainly is a misleading word (introduced by Bill Irvine, I think), but the concept is anything but trivial. It is also found in several other traditions, including medieval Judaism, 8th century Buddhism, and of course the Christian serenity prayer.
Yes, Epictetus puts forth a theory of selfhood, though I don’t really see the analogy with Paul and salvation.
He was also the most Cynic-like of The Stoics, and I’ve argued in my most recent book that his “disdain” for externals is tightly linked to the Stoic concept of Providence, which in turn hinges on seeing the universe as a living organism endowed with Logos. None of that is tenable given the modern scientific view, so it has to go. In a Field Guide to a Happy Life I show why and how: https://www.basicbooks.com/titles/massimo-pigliucci/a-field-guide-to-a-happy-life/9781541646940/
As for political involvement, the evidence is far more than cirucmstantial. Nero’s advisor explicitly warned the emperor about the dangers of Stoic philosophy. Cato the Younger — a Stoic role model — took up arms against Julius Caesar. And The Stoics, of course, are cosmopolitan, with Marcus explicitly saying that we should always work (with reason) for the common good.