DNA testing really has debunked a lot of absurd claims, hasn't it.
It certainly has. For example, DNA testing has debunked the claim that Prince Albert of Saxe Coburg-Gotha was illegitimate. His British Coburg descendants in the male line match the Y-DNA of other male-line descendants of his ancestor Leopold I, King of the Belgians so that claim has now been proved to be absurd.
However DNA sometimes confirms claims that were thought to be absurd, and those results are not always made public. Silence does not always mean failure.