Is it not obvious? Widespread ethnic groups are widespread due to this reason, Latin nations are all result of Roman empire's and don't share common descent. Even Germanics like English are Celtic by majority of their DNA makeup - even excluding them Austrians share more descent with "Central Asian" Magyars and Slavic Czechs than their fellow Germanic cousins from Netherlands and speaking of this even North and South Chinese have differences in genetic makeup due to different intermixing in the respective regions. Ethnicity above is the feeling of belonginess through shared cultures, language and habits. That's the logical result of natural human tendency to assimilate.
You should stop throwing this term British classification and should pick up better sources to back up your arguments. It was the British that classified disparate archeological remains as Indus Valley Civilization, the savages inhabiting were not equipped enough to even realize what archeology is and what it tells about their own origins. So, going by your own route of throwing this term, Indus valley is nothing but British farce, won't you agree?
Why didn’t the Hindus of India ever defeat an invading army!
This is the title of the thread, I didn't claimed anything.
LOL
Bajaur massacre - Wikipedia
There were more Rajasthan and (latter Maratha) based revolts than from Punjab during the entire Sultanate + Mughal period. Everyone wants to be the captain of his own ship, everyone likes freedom. Aurangzeb spent his all life fighting revolts of Rajasthanis, nascent Bharatpur-Dholpur state(s) of Suraj Mal and of course Marathas. I don't see much of conterminous Punjab in rising up in revolts, they were awkwardly docile lot once conquered.
What of the joining them? Second Mughal Emperor Humanyun who spent his life outside subcontinent (in Iran, Central Asia getting assistance against Delhi-Bihar based Suris) married a Delhi region based lord's daughter NOT any Potohari or any other.
Gazetteer of Ulwur : Powlett, P. W. (Percy William), b. 1837 : Free Download, Borrow, and Streaming : Internet Archive
What power center? When did the Punjab served as a power center (except during Sikh states)? Whom did they conquered? What did they built outside there lands? Where did they spread their culture/language? What native religion/sect they developed and spread? What advancements the courts of their Kingdoms produce? NIL, nada.
Look at us North Indians, from Afghanistan to tip of Tamil Nadu, from Balochistan to Nepal, everyone speaks our tongue. We ain't in the same league bro.