I'm overall pleased with the Harris selection (even if she wasn't my first choice), but I think a lot of people are underestimating Pence in the debate. Look at the VP debate in 2016. He swatted away everything Tim Kaine threw at him, and defended even the most indefensible Trump statements/positions through a combination of outright lies and calm. He stands a good chance at the VP debate because he is willing to say incredible lies without any shame whatsoever. These will be fact checked later but perhaps not in the moment.
Conversely, Kaine had a terrible strategy for that whole debate (force Pence to agree with Trump), and I doubt Kamala will make the same mistake. She has a record to hit him on now.