A couple of things: JD's a trained lawyer, the guy has "debate team leader" written all over him, Walz has a different background. On that front, it's just a mismatch altogether.... so when you get into that situation, do you play his game, or do you have to take a different tack and play to your strengths?
I don't know if it worked or not, but the overall point is that you aren't going to "outlawyer" a Yale law grad if you have Walz' background and demeanor. You have to do something else.... there was a bit of rope-a-dope in the strategy, and sort of falling back on the policy specifics that are more popular within his ticket's agenda. My guess is it all did not harm.
The second point is that while JD, as a forensic debater, looked the part well tonight, a lot of what he was asked to defend (ie. abortion, healthcare, J6) is *really* difficult stuff to defend. You can be a world class debater, but when given the task of defending Trump's position on abortion of his inability to accept election results, come up short. And I'd argue he did in a number of these exchanges, particularly on abortion and J6.