Bedrockgames
I post in the voice of Christopher Walken
It just seems that, as you’ve described it, most decision points for the fiction belong to the GM. Sure the players can go to this city or that area, but what they run into will always be what the GM wants it to be. How those elements respond to the PCs will be up to the GM. How social interactions will go is up to the GM, with perhaps some influence based on the player’s choice of description. And so on.
Just to take this one in isolation: this is an example of why terms like the fiction are a problem. But to answer as clearly: the GM controls the setting. The players have no control of the setting outside their character. So obviously anything that enters the setting is through the GM (though like I said, it isn't simply what the GM wants, there are plenty of tools, procedures, etc to help this process). But what happens is very much dependent on the players. The players decide what they do, where they go, and in this style they pretty much have free reign to go wherever they want. Like I said in my earlier example, if the party decides to start beating people up and stealing their money, that is where the campaign goes. Exactly how that players out will be a combination of player choice, the GM choice, luck of rolls, and concrete things like PC abilities (for instance a character with a particularly good non-lethal attack, is going to have a leg up in this particular endeavor). This is the kind of game where you very much are encouraging players to surprise you, and to work with those surprises. If the players decide they want to start a cult, that is what is going to happen. It is just the setting stuff (how the world reacts to that kind of choice, what challenges emerge) is in the hands of the GM. But there is responsibility there. You are not just unleashing your ego on the players.