I really don't think this winner or loser of the debate topic is all that relevant. Anything other than a total faceplant was a win for both candidates (particularly Harris). Harris didn't need to win the debate to help her cause. The post DNC polling was far weaker than most were expecting, and the most recent polling suggested waning support, notably in the rust belt. She just needed to silence the narrative that she was a poor debater/weak under pressure, and relay some semblance of policy, as she has been extremely vague on that thus far. She was partially successful there. Neither candidate really elaborated on policy. Although, to be fair, Trump doesn't really need to talk policy nearly as much, given we have a data point of his first Presidency.
The question is, how much will it move the needle for Kamala. I think it definitely stops the bleeding. But probably not enough to swing 3% or better in polling. I guess we will see over the next 2 weeks.