The original Commander Legends wasn't set in a specific setting within MtG, never mind a specific city, this one is.
Don't get me wrong, you are probably right to a degree, but I think it will be a small minority of characters that aren't "Forgotten Realms" characters, although I do believe Strahd did visit FR during the conjunction or whatever it was called in earlier editions.
The vast majority will be FR characters (including the greater FR area, not just Toril, but Realmspace, and connected planes/afterlives (Gods and other planar creatures tied to FR lore, like Lae'zel).
But I can see a few exceptions,like Strahd and Tasha, but I do expect them to get FR tie ins, because WotC likes to tossing others settinger stars into FR in general.
anyways either way like I said, CL1 had no setting or theme, CLB absolutely does, even abit of story to it I think (Baldur Gates broad story).