Coffee Addict, what pasuk?
Joseph, Sambatyon is a legend, and the tribes behind it are even more of a legend. At least Sambatyon is mentioned in the gemara. The idea that there are tribes behind it seems to come from the medieval fraud “Eldad Hadani”.
More Chessed, it’s an explicit gemara in Yevamos.
It is Time, there is no difference in opinion in the original sources. As I said, the gemara is hilchesa, not agadeta, so it is binding, and there is no contrary opinion expressed. The stories people have told each other through the ages are irrelevant when there’s an explicit hilchesa in the gemara against it.