Peninsular Arab DNA from Saudi looks like this: Natufian Hunter-Gatherer: 67.0% Zagros Neolithic Farmer: 21.2% Anatolian Neolithic Farmer: 7.6% Caucasus Hunter-Gatherer: 4.2%.
However, Palestinian Christians DNA looks like this: Anatolian Neolithic Farmer: 41.8% Natufian Hunter-Gatherer: 24.8% Zagros Neolithic Farmer: 23.2% Caucasus Hunter-Gatherer: 10.2%.
That is very very different. If the Palestinians were Arab, we would expect their Natufian to be around 67%, but it is not, instead it is below 25%. Palestinian Christians are clearly not ethnically Arab.
When Palestine became Islamic around the year 1200 we begin to see some foreign admixture. On the coastal plain the foreign admixture is usually Egyptian. In West Bank near Hebron and Jerusalem the foreign admixture is probably Bedouin. In the North near Tzfat the foreign admixture is minimal and believed to be Kurdish. On balance it is fair to state that Palestinians are in fact ethnically Israelite. The divide between the Israelis and Palestinians is on religious and linguistic lines only.