The "Harris" campaign was a continuation of Biden's ongoing campaign under a new candidate. They never had a chance to set their own messaging nor policy priorities. And although I too doubt it would have ultimately stopped Trump, it certainly would have allowed them to try to target younger demographics with their policy.
I also fear that the Democratic party's takeaway from the whole ordeal may be that America is not yet ready for a woman president. But any candidate would have lost under Harris's circumstances. And Hillary was just a terrible candidate. Yet because those are the only two woman candidates we've had for President and both lost horribly, it's easy to draw the wrong conclusion here that those are related.
I mean that planning a presidential campaign takes years, years which they didn't have. And beyond the time required to plan and refine the campaign messaging, the candidate needs time to train how to answer questions following it. They had no choice but to reuse all of Biden's preparation for these, and even then it still looked hastily done.