The advaita vedanta you are mentioning is one of the theory out of many other theories proposed which was based upon upanishad and vedas . The same vedas which has horrible form of castiesm in it. Even the upanishad which is seen to be as liberal contain horrible form of castiesm.

To burst your bubble , advaita vedanta is proposed by adi sankaracharya ( 800 CE- 1000CE ) who was castiest and his entire writings are filled with casteism.

Advait vedanta got famous for its theory of non-dualism which went to west by proponents such as swami vivekananada , Paramhansa Yogananada etc and got famous. But do Brahmanism has only advaita vedanta theory only? Infact, several sects have different set of theories proposed based on vedas. Such as of ramanujachārya who proposed vishnu as Ultimate Reality and proposed Vishishtadvaita Vedanta.

There are many theories proposed. But Adi Sankaracharya version got famous in west. We have many other school of thoughts apart from advaita vedanta which are based upon dualism .