You would have to not only mod up / down chariots to your own particular taste, but also weaken Egypt's starting economy. In a vanilla version, they can simple churn out full stacks without feeling the punishing effects of population loss (by recruiting an army). This is because of their considerably high population growth rates, population size and so on. Throw in a few overscaled units (bowmen, desert cavalry, chariots), elite units which are dirt cheap compared to their rivals (compare the price of Pharaoh's Bowmen to Forester Warband), and what you get is a steamrollering faction.