Youu haven't shown at all what (outside of the logic of the surrounding fiction) constrains the DM in forcing the story to go the way he wants to. Even @
Manbearcat concedes that there are no rules that totally safeguard against this.
Alright, I've got a few moments, here.
Just to be as clear as I can on this. I haven't made any conscessions about anything. My premise was that with heavy prep (which presumes granular setting and metaplot material, either created by the GM or digested via purchased module) comes greater investment in the material that has been prepped seeing table time. Due to this temptation, there is a greater chance of the imposition of metaplot and "setting tourism" (the focus of play moving fundamentally from the PCs relationships/ethos/themes to experiencing the setting in motion - which immediately or eventually mutes the dynamic of the PCs as protagonists) than there is with light/minimal prep (even if this prep is focused and has high utility).
What I stated prior is that sytem (play agenda and play procedures) and social contract do the heavy lifting when it comes to mitigating the prospects of that imposition of metaplot and that dynamic of "setting tourism." Can they reduce it to zero? What I mean by that is "is it possible to have the imposition of metaplot and/or 'setting tourism' emerge regardless of system and social contract?" My answer would be, "while it might be extremely remote, it is feasible."
For instance:
Take the Powered By the Apocalypse systems that [MENTION=99817]chaochou[/MENTION] and I have been using for our play anecdotes (Apocalypse World and Dungeon World respectively). These systems are at the far end of the "congenial/adversarial to metaplot and pre-authored, granular setting" continuum. How does it accomplish this:
1) The players roll ALL dice.
2) The resolution mechanics are unified, simplified/streamlined, and completely transparent (I call that "elegant").
3) The GM has explicit, non-negotiable instruction to:
a) Follow the Rules. Contrast this with White Wolf's Golden Rule or AD&D 2e's "Rule 0" whereby the GM is instructed to break rules, ignore rules, or subvert the resolution mechanics when their deployment leads to outcomes the GM doesn't want.
b) Fill the Character's Lives with Danger/Adventure. The system goes into great detail about how the guiding principles for play interface with reward cycle and resolution mechanics. This is Baker's "push play toward conflict" and "escalate, escalate, escalate" from Dogs in the Vineyard. * World games are designed to naturally do this.
c) Play to Find Out What Happens. This is literally anti-metaplot. The outcomes of play procedures naturally lead to a snow-balling narrative filled with danger and adventure. The system will actively fight you if you attempt to impose metaplot. It is easier, and more profitable, to let plot emerge naturally through the course of play.
d) Draw Maps, Leave Blanks. Completely adversarial to granular, pre-authored setting. "When you draw a map don’t try to make it complete. Leave room for the unknown. As you play you’ll get more ideas and the players will give you inspiration to work with. Let the maps expand and change."
So how would it be possible for a GM to impose metaplot and/or granular, pre-authored setting in a * World game? By somehow overcoming 1 and obfuscating 2 (so the techniques of GM Force and/or Illusionism can be leveraged) while simultaneously ignoring some or all of 3a-d (with c actively fighting you and making your job harder).
In essence, they would be eschewing the game's agenda, breaking the rules, breaking the social contract (unless the players are actually complicit or utterly apathetic), and making their life more miserable than it would otherwise be (because the game is fighting them)...for no good reason. So, one question would be "why the hell are you playing a * World game in the first place when you could be playing something more amenable to your play goals?" Another question would be "if your players are complicit, why again are you running a * World game rather than a game that is amenable to the table's social contact?"
Possible in theory? Yes. If you're comfortable with the contention that you're actually still legitimately playing the game (rather than Calvinball) after you've willfully broken it to pieces and turned it into an abomination of itself.
Accepting the immediately above contention as true, then we're on to; feasible in the real world? Masochists exist...so, I guess?