Some questions about the defense of Mormonism

I have some problems related to the defense of Mormonism based on DNA. Suppose it is successfully shown by Mormon defenders that the book of Mormon peoples could have existed in a limited area and did not make much of a ripple in the gene pool. (How that squares with the casualty numbers in the BoM is another matter). I take it that is the thrust of the Mormon defense on this issue. I don't see that this gets the Mormons out of the woods if, as is suggested by this statement by President Ezra Taft Benson (Eisenhower's secretary of agriiculture and the grandfather, I think, of Arizona Republic cartoonist Steve Benson), the authority of the living prophet is greater than that of the dead ones, and if prophet after prophet says that those people on the reservations running the casinos are Lamanites.