Sorry, a 78 year old was not the right person for the job in 2020, not unless you were gambling that he'd make it to 82 without losing it and it was known they wouldn't run again in 2024.
Expecting an 82 year old to campaign, and then make it it through their next term (which people do care about) is just pants on head stupid. And why in the absolute hell would someone that age want to spend their remaining time in a job that ages even younger people....ego I guess.
We'll never know if another candidate would be polling better, because all the money and support has been behind Biden. My money would be on a relative unknown (as Obama was) who can show some fire in a speech absolutely trouncing rapist felon Trump this time around....so go back to 2020 and pick one, with or without Biden's support. He's not a damn king. Pick almost anyone other than Hillary or AOC, just someone who hasn't already been demonized for years. But it's too late now, and in any case Joe ain't surrendering the car keys anyway.