Sure you could write it, but would it be true? I understand what the Brahmins were claiming was based on birth and birth alone, and the idea of somehow being higher on the ladder of reincarnation because of karma.
A Gentile could decide to follow the God of Abraham, Isaac, and Jacob, and could even become a part of the “chosen people.” Further, from my understanding, it wasn’t seen as a benefit that only they reaped from being chosen, but their covenant was much more strict than the covenant of the Gentiles. The superiority wasn’t in the people, but in their God.
Again, it’s a matter of necessity; the Messiah had to come from some people group. After the Messiah comes on the scene it all changes; the lineage and law (covenant) is fulfilled and now in Christ there is no Jew nor Gentile.