Biden’s in better shape than he was a few months ago, but I think a lot of pundits are overestimating how much this will really help Dems. He’s still decently underwater, and I suspect much of the recovery is from liberal skeptics of Joe who like his climate bill and student loan debt cancellation.
That's almost certainly the case, but his relative unpopularity seems somewhat irrelevant to Democrats running across the country. It would spell a wave based on a referendum on his presidency if Democrats were down everywhere, but the fact that individual races seem to be happening in vacuums within their own districts/states suggests he isn't as tethered to down-ballot Democrats as Trump was (and probably still is) in 2018.