Originally 5e and currently DCC, but Im in the throes of designing my own RPG.
but effectively the 'will' is simply to choose which pre-generated site to explore.
Having the players create the gameworld as they play in it is a very different thing from what Im talking about.
Collaborative worldbuilding isn't what I or my friends play these games for (namely because we all do enough of that without prompting, so its more interesting and less exhausting to explore what we've come up with, rather than to create something at the table).
So, what is the point of being a PC in this story
Thats up to the Players. The point of having a complete story is so that its still a functional story even if the players are entirely disinterested in engaging with it.
This is what I mean about embracing the will of the players. I don't write stories that fall apart if they don't participate, I write stories that can adapt to any level of participation they choose to take, up to and including zero.
No matter how it plays out, Ive got a good story.
It won't relate to them in any way whatsoever
Sure, because they haven't gotten involved yet.
And thats without considering if one of those introductury threads to pull is something related to a PC. Just because the story is functional doesn't mean parts of it can't relate to a PC.
But in any case, in terms of the subject of the thread, while not everyone may use the term 'simulationist' for your play, it is certainly fundamentally driven from the GM end of the table.
Its just another name for sandbox play, and its the entire point of the GM to be there and run the world, and at its best that world should be functioning regardless of the PCs actions, as otherwise you're not really running a sandbox. Its that philosophy that informed how I write adventures that can actually work in a sandbox.
But its again not one or the other as to who is driving the game. The GM runs the world and keeps the game reactive, as otherwise there is no game, but the Players alsos have to actually be there playing and making choices, or there is no game.