Even if you are a believing Christian (for whom the claim would be relevant), you would expect someone making that claim to demonstrate why it is true. I mean, if I walked up to you and told you I was the faithful and discreet slave of scripture, would you feel obligated to disprove it? Or would you ask why I believe that claim and how I can show it to be true?
After all, the JW interpretation isn't the only one. Why is their claim true while the others are not?