That "compromise" (as you label it) seems to refute your claim that "it makes no sense to me" that "The world in-universe is unaware of the rules used to construct the PCs."In that case what we have is a gamist compromise, one you occasionally have to make.
I put "compromise" in scare quotes because it's not actually a compromise. To describe it as a compromise is like saying that it's a compromise that the characters who figure in the film Star Wars are the ones doing the exciting stuff rather than (say) a mid-level Death Star operative who sits at a console making sure the nuclear reactors powering the thing remain stable; or (in Andy Warhol's remake) the same operative sleeping in his barracks for 8 hours after finishing a shift.
All fiction is authored. And hence all the elements in a fiction are there because an author chose to put them there, or because they are implied in some fashion by an author's choice (eg the presence of the Death Star implies the existence of engineers, even though we are never expressly told about them). But unless the fiction is a fourth-wall breaker (Blazing Saddles is the film example that comes to mind) then that crucial fact about the authorship of the fiction will not be something that is know by the imaginary people in the imaginary world of the fiction.
RPGs sharing this property is not a compromise. It's an essential feature of any non-absurdist RPging.