Manbearcat
Legend
The thing is, in my experience in practice it rarely is clear cut. The GM presents the world, with all sorts of details and events in it, some of them probably informed and inspired by character backstories. Then the players choose to focus on some aspect, and the GM generates more content related to that.
In my estimation, the appraisal process is less fraught than you're making it here.
Yes, it will entail developing first principles for analysis and yes, depending upon where play is in the maturation of its continuity there will be more or less disentangling of varying contributions (System, GM, Players), but its not some kind of inscrutable black box.
Whether you're evaluating at the level of the scene or at the level continuity-to-date, it can absolutely be done. Obviously, the former is less multivariate and therefore easier than the latter, but both can be done.
So here is an exchange I had recently with some friends, and I think its very operative to the discussion because it points at top-down agenda-based items and attendant analysis of how contributions shape play. I won't include the participants handles (none of them are contributors to this thread, by the way, but they are ENW contributors), but I will include myself. What do you think about the different pieces of this:
Poster 1: <Referring to their GMing of D&D 5e>...but it's also my responsibility not to upstage the PCs.
Me: You know there is a contingent of folks who would read that and say something like: "Its not about upstaging the PCs. Its about living, breathing, world. If the characteristics that animate the setting and the motivating aspects of NPCs/Factions are typically or always featured in a way that indexes PCs, then the world becomes sterile and flat."
That is what they would say and that is what they do say. They say:
"If a GM or system uses setting primarily (or exclusively) as a means to frame conflicts and render consequences around player-espoused interests (which index their PC's novel, assertive dramatic needs), then the world is inherently sterile, flat...and, by way of sterility and flatness...dead...unimmersive."
Therefore, the quiet part said out loud is:
"At some level of frequency and/or magnitude, it is essential for setting to upstage PCs."
Poster 2: Far far better for the player characters to feel sterile and flat.
You and I have had lots of discussions on this board. Of the people that typically disagree with me (and I them), I would say that you and I have had probably the most productive and functional discussions. I feel like I have an idea on where you come from at this point.
My sense is that you (a) definitely do not agree that Poster 2's statement is downrange of what you see me write. Is that correct? If so, I would say that is an essential piece here.
More interesting to me thought is (b) what is your appraisal of this 5e GM's assertion at the top? Further, (c) what is your appraisal of what I have written in the above exchange, both my Steelmanning of folks' position above and then my derived conclusion at the bottom?
I think that is also an essential piece of this conversation.