He barely won by 40K votes in 2020. If Biden stuck by the single term commitment the result could be different with an actual primary and the strongest candidate having time for a full campaign. That stronger candidate™ would have had more time to make inroads in PA and distance themselves from Biden completely.Biden would have done just as bad or worse, especially if he had another debate with Trump.
If it wasn't for COVID and George Floyd, Biden would have lost to Trump in 2020.
Kamala and the DNC had enough time to scope the landscape to deviate from Biden's most unpopular policies and all she did was double down on them.