Agreed. One of the great obstacles to the study of ancient anthropology is that much of our knowledge of various groups depends wholly upon the impressions of outside peoples who had contact with them; and whose prejudices color those impressions. They were often regarded merely as unimportant barbarians by the writers. This dismissive attitude by the ancient writers of history has affected how we viewed these peoples. Slowly, we're overcoming that prejudice - I hope.

Thus we know nothing about the Sea Peoples except the very little recorded in Egypt. We are just beginning to learn that some of our assumptions about the Celtic peoples were entirely wrong and based upon the faulty assumptions of the Greeks and Romans. As you pointed out, our Western impressions of the Mongols was skewed entirely by our limited encounters with the western Mongol groups and almost entirely devoid of information about others. This problem is very pronounced with the steppes peoples and others further east because there is so little archaeological evidence to work with to balance out the impressions, often mistaken, of contemporary writers. Their very cultures are a hinderance to study because they left so little accurate information behind. What they did leave behind is just now coming into better study, as our methods and understanding improves; and because the world has better access to areas formerly behind the Iron Curtain now.