The Biden question is important to me. It is likely important to other people, maybe just enough to affect the result. The whole thing smacks of nepotism. And that can be used against a Biden candidacy. Having said that, your explanation might be plausible, but the average soft D supporter is not going to buy into this story.
Polls won’t mean much in this election. Trump supporters are highly motivated to make the trip to the polls. D supporters are questionable. They say they will vote D to a pollster, but many can be swayed by a good advertising campaign to stay away. A lot depends on smoke-and-mirror shows of the last week of the campaign. And the 50% of those who don’t vote could affect the result in a D way, but will they come out? They didn’t seem to come out in 2018. If Mr. T wins, it will be razor thin victory (again). His base has no growth!
And it is possible that Mr. Trump could become totally unhinged between now and then. That could definitely change things!