Regarding reactions to the speech, I have no doubt that Biden benefited from some significant lowering of expectations, aided in no small part by Trump's campaign.
I think this point is under-discussed. Trump set up Biden as someone with mental degradation. When the actual Biden coherently strings a few sentences together, he looks good. When he has a decent speech, he looks amazing.
In short, it's a stupid strategy by the Trump campaign. Don't lower the expectations bar for someone who is not known as a great public speaker anyway. You're just doing Biden a favor.