Different disciplines tell different stories - do not "bend" linguistics to confirm archaeological or genetic findings. They may be different!
Historical linguistics
Genetics
Modern population studies
Ancient DNA
Archaeology
Historiography
Ethnography (Anthropology)
Historiography (historical Chinese records) should be used with caution and not overly relied upon. These ancient texts were not mainly intended to be ethnographies, but rather to serve political purposes. Names for ethnic groups are used to refer in a political and cultural, not linguistic, sense. For example, take the labels "Kachin" and "Shan" used in Myanmar today, or "Zhuang" in China. These labels contain speakers of various unrelated language phyla that have all converged culturally, and are viewed by others and sometimes also themselves as a single larger ethnic group.