I'm just going to pull parts of this out as best I'm able:
* Regarding model, D&D rules obviously aren't computer models that parameterize highly complex systems and run them from initial conditions. So that is out. My guess is that you think TTRPG rules serve as something like a phenomological model that gives (pseudo-) scientific expression to empirical relationships. I think a few games attempt to do so, but they generally yield a fair amount of sense spliced with a fair amount of nonsense.
So where I land on what TTRPGs can do (when designed well) is
generate an abstract mental model for the players to engage with; a rough user interface to put another way.
Players use rules holistically to draw inferences about relationships both within the imagined space and meta-relationships about rules intersections (because plenty of rules give expression to facets of play that exist mostly or wholly outside of the imagined space). That is what good rules do. They generate good, but abstract, mental models for individuals to deploy in play and for groups to share in their collective play.
* I don't know if
@pemerton disagrees with me on system having a "say" or GM's having a "say" in individual moments of content generation. And I definitely don't know if he would point to Baker as saying "mechanics don't author fiction on their own" as evidence for that. Perhaps, but I'll leave that up to him. Even if he does, I'm fine with it because I'm quite happy to have heterodox views persist in these conversations (either mine or others) so long as they're (a) not intractable and (b) able to be articulated and then interacted with sincerely and amicably.
But, rather than channeling pemerton or Baker, I'll just throw out my own throughts on the subject.
1) At most (not every, but most) moments of play, something novel is being generated and entering the imagined space for one reason or another.
2) Various participants, folding system into this, are responsible for this novel content being generated. An easy example of system (sans directly attached player or GM vetting right at the exact moment...if you go backwards in time, you'll find the signature of player or GM or both...but at this exact moment is what I'm referring to) having say is any of the following:
Event/situation-generating rolls like Wandering Monsters in D&D or Town/Camp in Torchbearer or Season-changing moves in Stonetop.
Codified state-changes like Doom Pools in MHRP or endgame in My Life With Master or all of the various "the scene ends here..." mechanics.
Condified and constrained menus of options like PBtA moves Read a Sitch/Person (and all derivative) or advancement schemes generally (pick x, y, z which generate novel play pending decision).
There are others, but those types of things are what I'm pointing at. And I don't see that they disagree with Baker's contention because I suspect that Baker's contention appends an implicit "in isolation" to the end of that. Content generators that are system-oriented or GM-oriented have prior participant (players included) inputs that will invest them with their purpose/place which engender the forward momentum/cascade to arrive here in the first place (where you call upon the system or GM to generate novel content). Further (and of course), you have the reality that this is all happening in the first place because all participants have opted-in to play the game in the first place.
I'll stop there and let you, or anyone else, mull that. I'll say beforehand that I don't know when/if I'll get back into this thread to formally respond to anything coming my way.