describing the setting as backdrop/context is not dismissing it as a source of colour and an element of the action, but rather pointing out that it is not the source of opposition, player-established concerns for their PCs, etc - it is introduced subsequently, to facilitate and develop those things.
What do you mean by "generic concerns" for PCs here? What would be examples of "specific concerns" for PCs? Generic or Specific to whom based on what? I'm just trying to get a better grasp of the conceptual language you're using here.
Could you also define "de-protagonisation" as you're using the term here? There is no current definition of this word at Dictionary.com or Merriam-Webster.com.
I like where you're going with Story Now I'm just not completely convinced it's necessary to bring along the construct of the Gamemaster. When we're discussing the evolution of TTRPGs, the GM appears to me as that runaway dog with its leash attached to a trash can: the owner thought tying the dog to a trash can would keep the animal in place. But, the dog runs, starts dragging the can, and runs even more because it's now terrified by this loud can chasing it everywhere. Maybe the trash can is the concept of Campaign, and maybe if players are grasping more control of the campaign, we can unleash the GM from it?