clearstream
(He, Him)
I'd like to explore one question in response here, without meaning to imply that other questions you raise aren't worth answering. Only that time is limited and I'd like to make progress on this strand.[MENTION=71699]clearstream[/MENTION]I am not following your point. Yes, as Vincent Baker has pointed out for a long time now, the core function of a RPG system is to establish what stuff gets incorporated into the shared fiction, and how. (I think this claim may need some qualification if we're talking about classic dungeon-crawling, but I'm not and I don' think you are either.)
How does that shine light on the function of pre-play authorship of setting by a GM?
But manifestly you have less agency over the content of the shared fiction then you would in a "no myth" game.
And more to the point for this thread, if the GM uses the pre-authored details of EPT to declare action declarations unsuccessful by reference to unrevealed elements of fictional positioning ("secret/hidden backstory") then it is the GM whose agency is pre-eminent.
I don't understand the second-last sentence.
As far as I can tell (by reading blogs, reading threads on ENworld, etc) most contemporary RPGing is not classic D&D, does involve rather extensive GM world building (either directly, or by choosing to use a setting authored by another), and does involve only modest player agency in respect of the shared fiction. As best I can tell, a significant amount of player action declarations have the purpose and function of triggering the GM to tell the players more about the setting (either by reading from notes, or by telling them stuff that is actually made up on the spot but that notionally is coming from the notes - "I did such a good job of winging it that the players couldn't tell!" is the typical hallmark of this sort of thing). And a significant amount of player choice is dependent on this - the players first get the GM, in effect, to provide a list of possibilities by narrating elements of the world, and then choose from among them.
Whether or not this is "fine" obviously is a matter of taste.
Premise - For player A to enjoy agency, player B must cede them agency over some aspects of the fiction, and vice versa. Sometimes ideas will come to both at the same time, but other times one will have a thing they want to express, explore, do or introduce, and the other will have to allow them to express, explore, do or introduce that thing. If B does not, for instance if B was always editing over A's contributions, then A can't really be said to have had agency.
Example - Bob and Alice have come to be (in their fiction) in a market. I won't worry about how they got there, but Alice narrates that she will buy a rosy ripe apple from the local orchards, free from the taint of disease or infestation, paying with one of the small copper bits common in these parts. I don't think Bob can at this point just get rid of those things, without eroding or destroying Alice's agency. Bob's agency over the fiction from there then, is to add to, transmute or expand on, but not deny or destroy, Alice's contributions.
That suggests to me that the question is one of who is doing how much of what, rather than whether or not there will be pre-existing contributions that some participants will concede a lack of agency over. Concretely, there will be such contributions, and for the authors of those contributions to enjoy agency, others must give up some agency, at least in respect of those parts.
Another Premise - After a time participants in a shared fiction come to naturally rely on elements that become canonical. Elements becoming canonical is a way that world-building happens. It's not all or nothing, and it can proceed organically. Tolkien worried about genealogies because they mattered to what he was focused on creating. Maybe Bob cares about such things, and Alice doesn't give a fig, but is happy to draw inspiration from Bob's contribution.
Another Example - Taking for this example a story-focused, freeform game that I created and played with others decades ago called Masters of Luck and Death (MOLAD), participants frequently made their own notes. My memory was good so I also kept track of a lot of things for the group. Additionally, I had the original creative idea, which other participants liked so much that they wanted to enter that world and create fictions within it themselves.
That suggests to me that creating fiction isn't and all or nothing thing, and it isn't impugned by being set within or using elements that come from somewhere else. It's as much an act of creating fiction to play out the life of a fictional slave in ancient Rome, with perhaps one or two twists but many authentic elements taken as canonical, as it is to invent the city of Ryme and play out the life of a chimney-sweep there. After all, chimney-sweeps existed outside of fiction to start with, so playing one is in a sense giving up agency: accepting something already made up for one.
Contemplating these sorts of ideas, it seems to me very clear what world-building can do for contemporary RPG. Whether that is principally the work of one of the participants or is the work of all, is a side-issue. It doesn't take away from its value. Concretely, where I am so far from having this discussion is that I can see that it is valuable to be flexible about that. Say I'm a principal participant - a GM - but Alice is into weather and comes to me with a weather chart for Ryme and suggestions for how that will impact on the unfolding fiction. Maybe weather with magical elements to it. That could become canonical for us.