I believe a more accurate term to use to describe a ban-worthy card is "polarizing": if a card is so powerful that the format forces you to build and play with it or build and play against it, completely preventing building and playing around it, then it should be banned. Skullclamp and Mental Misstep are examples of polarizing cards.

True-Name Nemesis is nowhere close to that, seeing how the format hasn't really changed outside of TNN being dominant, just like Goyf was the undisputed king of every format it was legal in pre-Green Sun's Zenith.