I've run into a lot of frustration wrt this issue and the kind of "historicism" that says, look Charlotte Bronte and Charles Dickens published books in the same year, obv. there's a connection there. But I don't see that the connection IS obvious, for precisely the reasons you've laid out here. I'd argue that the "of their time" thing is structurally reinforced by the way we periodize our history, emphasizing dates instead of personal contacts or continuities.