How could the bible be enough to use on a JW when they have been indoctrinated to believe that "Jehovah" is there in the NT 237 times? It's because they don't believe in the bible, they believe in the Governing Body's interpretation/spin of it.
If one chooses to believe in the GB, in spite of their history regarding failed prophecies and whip lash doctrinal changes, be my guest. Some people belong in cults. But its precisely why JW's are a cult that it is impossible to reason with them in general.
We are all responsible for who we put trust in. A JW, after being shown the evidence, if they continue to believe that the Governing Body is inspired, will no doubt do so. To that I say, it is sad. Very sad that a cult can so powerfully indoctrinate a person against real evidence, and real history.