A variety of political pundits and players (here, here) have made the argument that, if Joe Biden is not strong enough to be President for four more years, he isn't strong enough to be President from now until Jan. 20 of next year - 6 months. This is obvious nonsense, even if Kamala Harris now wishes it were true.
Had he continued to run for the nomination Biden would have spent the next 3+ months both running for office and serving as president. simultaneously. That is tough for anyone, and particularly tough for an octogenarian.
Do we have any sign that Joe Biden will do a worse job during his final 6 months than he did during the prior 6 months? Not really.
Without the added burden of travel and campaigning Joe should be able to finish out his elected term. In doing so he will fulfill a campaign promise of being a (one-term) "bridge" between the old Democratic Party and the younger generation of Democrats.
The argument for Biden resigning now is to shackle Harris with the unaccustomed presidential duties, making it harder for her to campaign. Advantage - Trump.
