First, Diablo's story has always been a load of nonsensial blabla. D4's story is really good compared to the rest of rpgs. The expansion is problematic compared to the original story: the narrator wants you to relate to some random Asian crybaby girl going around with an omnious object.
That's the stuff grown up men can't stand. I didn't like, most other people didin't like it, maybe a little girl somewhere could relate

Point is the story of the expac is subpar compaired to the base game D4. It is still inline with the other average rpg stories.