I agree that Zionist has historically meant many different things. Today it refers to people who support Israel taking land from Palestine.
I think Israel has a right to exist so long as it does not oppress its neighbors. Personally, I'd go with the one-state solution, with full democracy for everyone, and two official names for the state, Israel and Palestine.
1. Palestinian DNA tells a pretty clear story. Of course there was some intermingling in both the group that stayed in the land and the group that left.
2. Do you have any evidence for your claim about the Romans? I've never heard it.
Nor do I see what's illogical about the idea that the Jews who left kept their religion and those who stayed became Christians and Muslims. That would help explain the disappearance of the Sadducees and Essenes—Pharisees were more likely to go abroad.
3. Yes, antisemitism is ancient, But once the UN had chosen the plan, it's obvious that Jewish terrorist groups set out to seize all the land they could. People can be both victims and perpetrators, I trust you'll agree.