Oh sure. I suppose a tangent is a tangent, where as what I think is being proposed is not a tangent, but the expected content of play.
But I suppose that should be assumed whichever game or style we’re talking about. If I show up o a game of D&D and the group’s agreed to run AD&D and use the Giants modules, then I’m probably not going to create a character who’s looking for his long lost brother who was taken in by the Scarlet Brotherhood.
But if I’m playing Dungeon World, then that’s perfectly fine, and if the GM doesn’t bring that into play in some way, then that would suck.
I think where we (potentially) run into issues is with a game where the goals of play are a little more open, and maybe play expectations aren’t exactly clear. So a game like 5e with a GM running non-published material, and saying it’ll be a sandbox....and then a player creates a highly specific goal for his character only to find that the GM’s already filled the entire sandbox. That kind of thing.