Again historically speaking Jews were not there first in Palestine. According to Biblical mythology, some Iraqi Jews settled Palestine 3000 years ago for a short period of time. That doesn't mean Palestine should belong to every person of Jewish faith 3000 years later. No people in human history ever made such stupid claim.
Genetically speaking the Palestinians of today are the same descendants of the Christian/Jews population that had existed in the Levites for thousands of years who upon the Islamic conquest of these lands reverted to Islam and have remained as such till present times.
As for Palestinian Arabs, if you say they came from somewhere else, say the Arabian Peninsula for example, which is rather a very popular lie within pro-Zionism circles, then you have to prove it. Since historically there are no such records of any mass population transfer from and into Palestine under Muslim rule, or any mass genocide against native population of Palestine that were later replaced by immigrants from Arabian Peninsula, then Palestinian arabnized people are the rightful owners of Palestine. Which is also supported by genetic evidence.