You’ve got the polarity of that conversation wrong. Biden’s entire campaign is built on the notion that he will return character, ethics and judgment to the White House. Trump can very quickly derail that narrative and stomp on the O’bidenbama member berries with Biden’s own voting record, and Hunter Biden.
Trump can't effectively use that as an attack, because if he does it's an admission that his own administration is deeply corrupt. Oh, I'm sure Trump will lie about the severity of his own problems, but it's pretty hard to pretend that he didn't pick his daughter and son-in-law for roles simply because they were family.
Again, the only people likely to respond to the "but Hunter" diversion are those who are willfully blind to Trump's behavior and thus already inclined to vote Trump. I can't see it costing more than a small number of votes, maybe to those "they're all the same" false equivalency types who either abstain or vote for a third-party candidate they know won't win.