I think most historians are pretty well aware of how sophisticated ancient cultures were. The main parts where they're biased are:
*Rousseau-like ideas of hunter-gatherer cultures being idyllic, peaceful, and egalitarian. This is more of a problem with other fields and is basically the entirety of anthropology.
*Assumptions made from limited archeology and written sources. "We found an elephant coin and elephant statues. They must have worshiped elephants."
*The post-Enlightenment concept of the "Dark Ages" where Medieval Europe was full of drooling idiot Monty Python peasants wallowing in mud, and the Catholic church waged a war on "Science" until the "Renaissance" meant people were allowed to look at Greco-Roman statues again and the Science score went up.