Taking you literally, doesn't that mean that Islam may only be meaningfully defined in function of said historical context?
Yes; I think the Islamic message was always supposed to be universal through all ages and the Prophet and the early followers as examples of how both an individual Muslim and the communal "Ummah" are supposed to structure life and society.
One of the consequences being that they are fully entitled to embrace peaceful and enlightened attitudes, regardless of how well-supported more violent takes might turn out to be?
In a religious person's worldview, not always.