cofty: If anybody would like to play Devils' Advocate on this I would be interested
Your reasoning is interesting. The trouble is it assumes that you or I or anyone else could get a JW to carefully and critically examine their own beliefs for coherency, continuity, consistency, logic or any number of reasons.
If we could get them to do that, there would be no need for such subtle arguments such as the ones you put forth in your OP.
Since it is nearly impossible to get most JWs to see even the most glaring of problems with their beliefs, I do not believe you will be very likely to get them to examine this controversial doctrine with the thoughtful care that your argument requires.
When someone is ready to question, they will do so on their own. They will generally start with the loose threads which their own mind calls to their attention. Once they start tugging on those threads the whole thing quickly begins to unravel.
All that being said, I do appreciate the thoughtful approach you have given to this issue. I know it is something you have carefully considered for many years.