#2 Success in Championship reigns

Only a few superstars in WWE can look credible without championship victories. Big names like John Cena, Brock Lesnar, Ric Flair, and even The Undertaker had been successful only because of major title wins.
The Fiend does not need a title to look strong initially, but as the time progresses it will look odd to see such a dominating character without a title win. A title reign is required to establish himself as a main event level competitor.
Sting in WWE once again? More details HERE
Moving from one victim to another in a quest to purely conquer them looks to be the motive of the character, but it will become monotonous at some point. What will refresh things ultimately for the character is a championship storyline.
If done well, then there is no stopping him from achieving long-term success with the company. When the time comes for the creative team to consider giving him a title reign, they should not look back.