Yes, this is exactly it. We have tons and tons and tons of documents from ancient Greece and Rome. On the other hand, we have much more writings on Persia writt

Yes, this is exactly it. We have tons and tons and tons of documents from ancient Greece and Rome. On the other hand, we have much more writings on Persia written by Greeks and Romans than we do on Persians written by Persians: most of our knowledge of ancient Persia is via the Greeks and Romans! The sad reality of history is that having contemporaneous writings by the people involved adds a lot more color and detail to history than archeology, so people are naturally more interested - there's more that can be known!