I'm claiming that most of the people who call themselves "Palestinian" are descended from people who lived elsewhere before 1948. They are no more "indigenous" than the Jews who migrated after 1948.
You haven't supported that claim.
I agree that the claim has not been fully supported. The migration records for the time period between the mid 1850s and 1948 are notoriously incomplete, self-serving, biased and riddled with errors.
It is self-evident that there was a good deal of migration into the area by both Arabs and Jews in this time period. It is amply evident that Palestinian nationalism (as distinct from Arab nationalism) grew in direct correlation to the conflict with the Jewish people and their growing nationalism.
It is also quite evident that there is a double standard held by those on Team Palestine that Arab immigrants from Syria are "natives" and Jewish immigrants from Europe are "foreigners". But its also easy to see why. Arabs are same, Jews are other. But it should also be relatively easy to why the Jewish people bristle at being labelled as "foreigners" in their own ancestral homeland.
The bottom line, however, really is that it does not matter. Who lived where, when and who immigrated and when and who has "legtimacy" and who does not -- are all red herrings. None of it affects matters of sovereignty, legality or social justice.
We need to stop examining the past for ammunition as to why the "other" should have no rights today, and start looking forward to how we can provide social justice to BOTH peoples today.