These two weaken the other accusation.
Correct.
Investigating these absurd claims makes sense. In the case of a single accuser, like Ford, it is always helpful to determine whether or not there are any other legitimate accusations. A single accusation of abuse is not as substantive as if there are multiple accusers.
Once it is established that there are NOT multiple credible claims of abuse, then the question devolves into the evidence presented by the only accuser. Is it credible or not? It's hard to imagine that an unbiased view of Ford's evidence could EVER be considered credible. Therefore the conclusion becomes incredible by unbiased evaluation.
Ford will be isolated by this and will need to substantiate more than she has to make the claim against Kavanaugh credible.