By the time Biden dropped out, yes, she was really the only choice, logistically. I think at that point, 3 months ago, there was basically nothing the dems could have done to have won this. They could have made it closer, but any real shot at a candidate people liked, would have needed to have gotten spooled up a year ago, at minimum, two years ago ideally.
The DNC shares so much blame for overall strategy of the last decade+, but the decision for Biden to insist on aiming for a 2nd term the whole time, despite pressure, and only cave when the saw just how grim those final projections really were, is mostly his, personally.