Here's what I think happens (at least with the more logical minded folks):
When preparing to debate something with your adversary, you anticipate many different angles...all from a logical point of view. You can argue certain pet peeve subjects every which way from Sunday...logically and analytically...in your head. You can even have some of the more obvious JW argument busters ready...
but then... along comes the JW elder/friend/family member and they don't stick to the script that you've written in your head. That's basically what you've done...written a play with an imaginary person who thinks like you do now... but most JWs don't think logically...if at all. They react and they react with the pre-programmed responses from the WTS. Even when you think you know those reactions, they then jump around on you. They bring up shit that ain't got nuthin to do with the subject at hand and before you know it, you're off arguing on something that has nothing to do with what you wanted to talk about...and quite frankly something that you haven't really researched that deeply.
So in the end they come off looking like they put you in your place because they managed to divert the conversation/debate to an area where they take charge.
What you have to do is stick with just one (or at most, two) subjects...subjects that bug you the most. And know them inside and out. Become an expert on it. And if/when you do get in a discussion again, you stick to that one subject and you don't allow them to deflect the argument. JWs are masters at deflecting. Not so much because they're good at it or well trained at it...it's a natural defense mechanism. When you get backed into a corner, you look to get out of it, so you deflect attention and hope to escape. When they start to deflect, you can know that you're going in the right direction. So you have to keep the pressure on and don't let em slip around and outflank you with "But where will you go" shit reasoning.
But even then, you ain't gonna win nothing against a JW that wants to believe. They're too indoctrinated. Only when someone is questioning or doubting themselves will they look at evidence against their belief system. Good luck anyway...