That is pretty much a description of the end many big wars had in antiquity. Unless we are talking about big states, total defeat with total annexation and middle to long-term assimilation was always on the table. Take Rome VS Carthage, it took them 3 wars, but Carthage did end up completely destroyed and assimilated, to the point of having Romans salting the earth of the defeated city. Take all the tribes the Romans conquered in Spain, Gaul, all the cities with their own culture, religion and organization that Romans conquered in Italy, etc.
It was a matter of survival.
You did end up picking a conflict of which I honestly know nothing source-wise, because it is a Greek thing and I am more of a Roman mentality and memory kind of guy. What I can say is: regarding the enemies Rome conquered? I don't know of any (besides the guys from Greece,but even those boarded the Roman train pretty fast, and even if Roman and Greek sources do have their differences even hundreds of years later, Greek authors did ended up writing from the perspective of the Roman world). The lusitanian, iberian, celtiberian, gaul, german, britannian, illyrian, dacian, etc tribes didn't left any kind of narrative concerning their wars with Rome. Carthage didn't left any kind of written records narrating their war with Rome, I don't know of any Egyptian records regarding their fight with Rome, nor do I know of similar sources from the Asian kingdoms conquered.
Having so much Latin and Greek sources surviving until our days is already pretty impressive (even if they are a small drop in the ocean of Latin and Greek literary and record-keeping production), having them for the people Romans conquered is practically impossible. Losing a war and being conquered wasn't that big of a leap, and being conquered being a medium to long-term extinction event wasn't that off the mark in the huge majority of the cases.
I think this is indeed the case. None of us is really wrong, we are just using different experiences with the subject to achieve pretty different answers. The consequences of defeat, and the nature of historical self-narrative, changed quite a lot in the last 500 years when compared to the thousands of years before.