No, you are wrong. At this moment Biden would still be the candidate without the debate. That is what allowed the removal. It gave the rats the hammer to beat him with.
Personally, I have always believed that the Democrats expected to lose in 2020. That's why all the younger and more ambitious candidates dropped out before Super Tuesday in favor of a senile old retard who was old news in Washington 20 years earlier. He was supposed to be the 2024 version of Bob Dole.
It was the COVID fiasco -- which began almost immediately after Biden effectively secured the nomination -- that even made the 2020 race a contested one. In some ways, the timing couldn't have been worse for the Democrats.
Notice that they've been calling this the "Biden/Harris administration" since even before January 2021.