Keep in mind that JWs are given very basic and rote preparation for defending their faith. They can anticipate some criticism and have a few Bible verses handy, but they also are taught to get away from anyone trying to 'teach' them or asking them to question their beliefs. And this works, because so many people are equally unprepared to challenge JW beliefs (or defend their own).
I was never confronted by someone who really challenged what I believed. If I had, I'm sure I would have come out of it a complete mess. Having the very neat and tidy JW belief system picked apart would have probably been traumatic for me. Instead, I had to deal with the occasional person who challenged one or two points and was easily parried. It gave me a false confidence that I had the 'True Truth.' But it wouldn't have held up against a targeted attack, so to speak.