It does nothing to demonstrate that Mormons are overall worse people than atheists. It is only a single point in the atheists' favor.

I think these two sentences are contradictory. If it is a point in favor of the proposition that atheists are better in some regard than Mormons, then it does something to demonstrate the general case, if only weakly.

Rationality is not about reserving judgment until ideal evidence is available. Rationality is incorporating all the evidence at your disposal. I agree that most of the evidence available is mixed and weak, so it shouldn't be overweighted, but it is still relevant.