I believe there's a misunderstanding here regarding the meaning(s) of the term historical accuracy: Nightmare tends to view it as "historical accuracy as in chain of events that actually happened" whereas others see it as "historical accuracy as in realistic social/natural environment for the time period and realistic, plausible possibilities of development after 272 BC". For instance, the Persian reforms of the Hai faction never happened in real life because Armenia got caught up between Arsacid Parthia and Rome and ended up being a semi-autonomous kingdom ruled by an offshoot of the Arsacids. But if things had gone differently (say, a power vacuum that makes it possible for Armenians to conquer Iranian core regions), the "reform" might actually have happened because of existing dynastic and cultural ties, not to mention geograpic proximity. Seeing as the human player starts the campaign in 272 BC, he or she can avoid the mistakes made by historical characters and thereby build a prosperous empire.
By the way, both EB I and II only include factions that had a disposition to and a realistic chance of becoming a bigger power of sorts.