Ashenazi jews are just one type of Jews. And there is no evidence of this distinction existing in antiquity. Even a token physical examination of self-identifying Jews shows you are of mixed heritage. (not a crime, true of everyone) Arabs made up the vast majority of the population of the Levant prior to the formation of the modern Jewish state.. Using your argument of using modern sampled alone would make them the “real” Jews
The way credible scientists actuality check is using ancient samples then doing a comparative analysis with modern. Scientists have already done DNA analysis of ancient Jewish DNA and compared it with modern. There is academic consensuses you are not racially pure descendants of ancient Jews. but this doesn’t mean you aren’t connected at all. You have some DNA from the Levant. You choice of culture and history connects you,
This is primordialism view of history which not all academics accept. The alternate of modernist historiography is also popular in academia (mostly in the humanities) Modernists argue since no one is racially or cultural pure ethnic groups and nations are “imagined communities’. You just think you are Jewish because you imagine it (nor I Greek). This is very popular among leftist academics as it fits in nicely with their antinationalist ideology. (also see gender is a “social construct”)
This incidentally was one of the arguments that was used to justify tthe claim the former Yugoslavians are “Macedonians”. Greeks were demoted into an just an imagined community not a “real” ethnic group. Meanwhile the former Yugoslavians are apparently now “ethnic” Macedonians and antihellenic founders of the Hellenistic period… which defies even basic common sense.