I haven't heard that track, so my comments are general, not specific to that cut.
I couldn't disagree more - I love Mac Rebennack's voice. I've always wished I was a better singer, but the kind of voice I would want is more like Dr. John than Frank Sinatra. I do agree that his voice is perhaps not well suited to ballads - or at least, better suited to blues and R & B.
We agree to disagree. I've always felt that there were dozens of singers in New Orleans who could put him to shame.