That's different, he's supposed to be a spy that everyone thinks is a Vashoth. Pretending to be one who has left the Qun isn't feasible when you're still acting like you follow the Qun. He needs to act the part to fulfill his role as spy. And he still has superiors, the Inquisitor doesn't.
Not true. The background is about how you start out. What you choose from there is up to you. The Arishok gives me a role. He says travel to Orlais, pretend to be a Vashoth, spy on the chantry there and report back. So I join up with a merc company, I'm there when everything goes down and they make me Inquisitor. I should be free at that point to either fulfill my role, continue to pretend or make the decision that the circumstances have changed my role.
Even beyond that making it so you can't follow the Qun basically rips the culture from the Qunari. If you have no exposure to the Qun and we don't even have the option of being a follower what's the difference between a Qunari and a human besides horns? It seems like the uniqueness of the experience will be people not trusting you because of how you look. But the reasons they have for not trusting you will have nothing to do with a culture you identify with. If I'm an Elf I'm Dalish/City and all the reasons humans hate me make sense and I can identify with them. If I'm a dwarf with the Carta all the reasons humans will be distrustful of me make perfect sense. But if I'm a Qunari with no exposure to the Qun and no real sense of the culture of my own people then where's the connection? From where I'm standing culture wise they're handicapped.