JD Vance yelling at his kid is a weak argument if true. It fits into the category of Trump is an asshole and that's not proven to be a politically successful argument for Democrats. Voters, swing voters in particular, already know Trump is an asshole but don't seem all that bothered by the cursing, name calling, and jerk behavior. Hillary's campaign focused a lot on the Trump is a mean jerk narrative and it didn't seem to work with swing voters nor motivating the base.
The better arguments against Trump and Vance I believe is that they are phony working class populists who are out of touch and only care about themselves. People who are too radical and too extreme to be in the White House. Agents of chaos and calamity. Those are better arguments to be making than Vance was a jerk to his kid imo.