I can't see how the fact that Palestine hasn't been an independent entity is relevant to anything. There are any number of countries all over the world that weren't independent entities until they won their independence. In fact I get the impression that outside of Europe there are relatively few existing countries with that kind of direct continuity.

How many countries in the Americas were independent countries within before they were established in the last couple of centuries?

What matters is whether the people have a shared history and a shared identity - and there is no doubt that at this time in history the Palestinians have that.