Is a champion who reigns and doesn't defend agaisnt his #1 contender a paper champ?

A long-term champ who never faces his mandatory can't be considered a paper champ, as there may be other factors involved. However, it it's the same mandatory I sure would consider him a paper champ.
You can't call yourself a champion if you're not willing to face the legitimate 'next best' guy every so often.

 

WE all rember the day when paper champ Lewis was strip of his title for failing to fight Ruiz, when he decided to fight lesser foes like Grant, Tua and Tyson.