Citation needed.Well, there is a small number of them. King Lich could just take souls from Bvonsamdi and Helia. They are not his level.
And once again that statement has little meaning if it's not clear how many beings were considered. Out of the millions of people living on Azeroth, that statement could have taken into consideration 30 creatures, which means that even someone like Kael'thas or Varian would appear in that list. That extremely vague statement doesn't exalt the Lich King's power at all.the Lich King is one of the most powerful beings on Azeroth. So who are the most powerful? Old God.