In typical RPGing, there are two main ways to work out what happens next. One is for the GM to just tell the table. The other is for the players to declare actions for their PCs, and for those actions to be resolved using the game rules.While there is a lot to be said about the social contract & expectations of players, your particular objections seem to be driven by extrapolating a powergaming playstyle of D&D should be applied to fictional settings of D&D. This is a fairly fundamental question: What comes first, the rules or the fiction?
I don't really find a rules-over-fiction gaming style to be particularly compelling or even well-evidenced. Every D&D rulebook, setting, novel published over the history of the game features quite a lot that contradicts the view that rules should take priority over fiction
A game "set" in an established world like Eberron, Forgotten Realms, etc. has certain elements to it that players can and should expect to be present. Local & national powers in these worlds must have some means of keeping control over their territory over years, decades, centuries. If players can easily upend the existing order this is almost breaking the social contract of the game since, regardless of what the specific numbers & rules may say, this isn't something that is in accordance with the common expectation of the setting.
I understand @Tantavalist to be assuming that the second method would be used, and - in my view correctly - observing that if it is, then in standard D&D there is no prospect of high-level and maybe even mid-level PCs being defeated by ordinary people, assuming those people are statted up in a way that is commensurate with their established place in the fiction (which includes needing the PCs to help them with their problems).
I can easily imagine a D&D game where the players agree to play their PCs like Superman - ie they agree not to use their powers to disregard or even overthrow the existing social order.
But if the players try to have their PCs do that sort of thing - and it's a fairly obvious fantasy fiction trope (REH's Conan does it by conquering Aquilonia, kidnapping the ruler of Vendhya, etc) - then when we move to the resolution of those declared actions I think Tantavalist is right. I don't see how an abstract notion of fiction before rules is going to do any work. Unless you're proposing that the GM should just ignore those action declarations or declare by fiat that they fail.