It seems to me that at times there is a temptation to use tragedies to try to further the ex-JW agenda of proving Watchtower doctrine wrong, and in my opinion by using an apostate strawman argument at that.
Yes, they pump up the experiences when someone (allegedly) escapes harm when they are at the meeting instead of staying home. But JWs are never directly told (nor in my own anecdotal experience do many actually believe) that they have physical immunity from harm while preaching.