There's definitely a perception among most people outside of the party activist bubble that Biden is a do-nothing President (at best) and an incompetent senile fool (at worst), regardless of where the truth actually lies. Perceptions matter a hell of a lot more than the facts on the ground, and Democrats need to come to terms with this fact.
But shouldn’t these voters still come home to him?
Some of them will because of Trump, yes.
But there's definitely also a lot of people who are disillusioned enough with Biden's uninspired and 'boring' image (particularly young voters) that they may just stay home or vote 3rd party in 2024, even against Trump. Regardless of how true such a paradigm actually is, a lot of young voters (especially young leftists) see establishment liberals and Republicans as being nothing but two sides of the same corporatist coin.
American politics is something that's very easy to get disillusioned about in the modern day, and you're not going to win many favors by trying to explain Modern Monetary Theory to someone who's complaining about their leaky roof.
I’d also argue that 2024 Trump isn’t as compelling a villain as 2016 Trump was to these voters. Trump in 2016 was more infamous for his views on POC and women rather than his stance on free and fair elections.
Also, won’t Trump have a similar enthusiasm issue regarding some of his soft supporters?