Hellenism Salesman
Emperor
gonna agree here.I'm the type of the person where the realism in the system doesn't really matter to the game.
It needs to be only "fairly believable" and "immersive" but not necessarily realistic or historically accurate.
We should always strive for greater accuracy, especially as the game reaches more and more people. However, with a game as complex as Civ with so many different production requirements (art, UI, design, sound, music, and then the history on top of that), I'd imagine Firaxis might give themselves a "realism quota" and just try to meet that across the board. That means that the individual systems might not be perfectly accurate, but when put together they give the impression of accuracy. Verisimilitude and all that.
Even though I doubt that's how they actually see things, I at least feel confident that we'll never get a 100% accurate Civ game. We can strive for things to be better and better, but little mistakes, intentional disregard, and just plain old ignorance keep it out of reach.
I fully admit I'm rambling a bit (it's late as I'm writing this- forgive me

As for now my sleepy head doesn't have an answer but I can tell there's some fun decisions to be made in the balance between fun gaminess and realism.