Pretty strong cases have been made that the Han Chinese ethnicity is an invention. This makes some sense given China's pre-CCP plethora of wildly different languages, and quite distinct appearance differences between provinces. That's hard to explain if one adopts the "majority ethnicity" view. Of course, from a practical perspective, once everyone believes the myth then it's a de facto reality
"Han is a social construct" doesn't change the fact that they operate as a de facto ethnostate that keeps foreigners out and their more phenotypically distinct ethnic minorities out of power.
https://www.hrichina.org/en/content/4573 http://foreignpolicy.com/2010/04/13/the-myth-of-one-china/