Read more about Shadowlands ➜ https://worldofwarcraft.mgn.gg
The entire point of Sylvanas defeating the Lich King in one-on-one combat was to show how powerful she has become since joining ‘the maw covenant,’ and to establish her as a threat even greater than Arthas was…and, by extension, to make us realize how much of a threat the Jailer is if HE is.
source