I think the people who bring up the enthusiasm difference are forgetting one key factor, and yes, it is a variant of TDS.
People might not like Biden, but they'll vote for him just to get Trump out of office. They're not gonna go out and get a sign, or attend one of his rallies, or whatever, but they'll still vote for him if it gets Trump out of power. They think that he is the reason everything has gone to shit, unjustifiably, or not, and incorrectly think that voting him out will fix it. To them, it's like going to the dentist to get a root canal, or something. Yeah, it sucks ass, and you're not excited, or enthusiastic for it at all, but it's for the greater good, so-to-speak. Better take care of it now before it festers even more.
They don't screech about Trump on Twitter, or whatever, they're the opposite of those folk. They're sick of the screeching, and just want people to shut up, and think that if they vote for Biden, they'll finally have some peace, and quiet again. They're wrong, but that's probably what their mindset is.
This is why I still think it's too early to call this race yet. Biden might've shot himself in the foot repeatedly over the last few weeks, but TDS still might be enough for him to win. I'm not trying to be a doomer, or anything. I just think it's something we should keep in mind.