Scientists have come to the conclusion through comparison of genetic samples of different Jewish groups such as Yemenites and Ashkenazim that Jews and Samaritans share common ancestry, which isn’t exactly congruent with the fact that Chazal considered them converted Assyrians. Is it possible to say that there was a pre-existent group that shared Samaritan beliefs and later intermarried with the kuttim? If not how can this be reconciled with the torah’s narrative?
Beyond this I want to know how the kuzari principle can hold in light of the history of Sammaritanism as a religion. If you go by our chronology, the Samaritan population illegitimately converted and were all convinced that they were the original Jews and they were in fact present in Ancient Israel and broke off from mainstream society during the time of Eli to form a distinct group. By the Kuzari principle such a story could not be fabricated for the same reason that the story of matan torah could not be fabricated, so how can this be explained?