In The Kite Runner, why is Assef still treated better than Hassan even though he's a foreigner?

Hassan (the son of Baba's servant, Ali) is a member of the
ethinc Hazara, who are scorned by most of Afghanistan's other social groups. The Hazaras
were generally poor and uneducated (as was Ali and Hassan) and most lived in the
mountainous region known as Hazajarat. They would eventually become one of the prime
targets of future ethnic cleansing by the Taliban. Assef, though blonde and the son of a
German woman, is nevertheless one-half Pashtun--the ruling ethnic group in Afghanistan.
His parents are wealthy and powerful, thus enabling Assef with the belief that he comes
from the ruling class of the land. Combined with his German heritage and love of Hitler,
Assef considers himself and his family to be better than most--and certainly more
privileged than any Hazara. His German roots may have helped his own rise in ranks
within the Taliban, since Hitler's Nazis were defeated by United States--a prime enemy
of the Taliban. In any case, Assef's Pashtun roots gave him a higher social
standing than Hassan.