Kel'Thuzad is a quite good necromancer, and I also think that Anub'arak "should" have been very powerful, canonwise.
The real problem is the huge idiot ball that the Lich King had during the whole WoTLK expansion ^^'
Maybe even here, the Lich King will let Kuja totally destroy the Scourge, believing that he can defeat him and reanimate him to have the strongest fighting force of all the times... I bet even Hogger would have been a better Lich King that Arthas :P
__________________ If you are not merciless, your soul will be slaughtered!