As to who the arbiter is, well nobody, its not a difficult concept and its one with a very, very long history so I dont think it needs an arbiter really. But I think the Chief Rabbi is as good a guide as anyone. 'Zionism is nothing more or less than the near 4,000-year-old expression of the Jewish People’s connection to, and right to self-determination in, the land situated at the very heart of Jewish faith and peoplehood.'
'Chaim Weizmann, who would later become the first president of the State of Israel was once asked by a member of the House of Lords why Jews were so fixated on one tiny, contested piece of land. Were there not other territories in which a Jewish state could be established? Weizmann responded that this would be like asking why he had driven 20 miles to visit his mother, when there were many other perfectly nice old ladies living on his street.'
He also says 'Zionism, which upholds this right of the Jewish People to a national home in their ancestral homeland, is undoubtedly best served by a peaceful future for both Israelis and Palestinians.' Other zionists may disagree. That doesn't mean he isn't a zionist or that the definition of zionism has changed.
'I am a Zionist because I believe that alongside the world’s 157 Christian-majority countries and 49 Muslim-majority countries, there is a vital need for a single Jewish country. I am a Zionist because I am committed to the idea that even in a place where conflict has reigned for centuries, peace is achievable and worth fighting for. I am a Zionist because I have inherited a language, culture and faith from the indigenous people of Judea. I am a Zionist because over thousands of years, my ancestors recommitted daily to holding Israel at the heart of their faith. I am a Zionist because I am a Jew.'
www.newstatesman.com/politics/religion/2024/10/what-is-zionism