#3 The Undertaker is not a Grand Slam Champion
Well, this is pretty much an aftereffect of him never winning the two mid-card championships, as mentioned in the last slide. The Undertaker, despite being referred to many as one of the greatest WWE Superstars of all time, is not a Grand Slam Champion.
In case you don't know, a "Grand Slam" is an accomplishment recognized by pro wrestling promotions when a wrestler wins a set of specific championships throughout his career. WWE has had two formats for the Grand Slam, the first of which included a Primary World Championship, a Tag Team Championship, a Secondary Championship (Intercontinental), and a Tertiary Championship (European or Hardcore).
WWE revised the format of a Grand Slam in 2015, and the new format requires the Superstar to have won a Primary World Championship (WWF/WWE/Universal), a Tag Team Championship (WWE/RAW/SmackDown) and both the Intercontinental and United States Championships.
It's tough to imagine The Phenom going after these titles anymore. But the reports suggest that WWE has signed him for a contract of 15 years, so you never know! Still...very unlikely!