Placeholder does not necessarily mean he won’t run. Biden’s value is that he’s owned 100% and will do exactly what he’s told for as long as he needs to do anything at all. Then he can be hidden away, perhaps in perpetuity, like RBG.
FWIW, if the Ds win the Grand Slam of P, S, and H, I expect the American equivalent of “Gesetz zur Behebung der Not von Volk und Reich” (the 1933 Enabling Act) to be quickly passed - with rule by “Presidential” decree and de facto “One Party Government.”
Recent developments have been a softening up exercise for just this eventuality.