Let's set aside the multiple issues with "I think one of my distant ancestors lived here 2000 years ago, or maybe just other members of my religious group, therefore I have a right to live here today" and assume that yes, that sort of historical/ancestral claim gives comtemporary Jewish people a right to live in Palestine. Even in the most generous light imaginable, it would not give them a right to build an ethnostate by committing genocide on the current inhabitants. Israel is so far past anything that could be reasonably granted from ancient Jews living in Palestine that there is no possible defense along those lines.

Or are we strictly talking about western powers giving the Jewish people a 'homeland' after the second world war and the holocaust?

Yes, that's what people mean when they refer to Israel as a colony of Europe/the U.S.