Remember everybody that in Warcraft III they fought to a standstill none could gain a advantage, but in Warcraft III frozen throne Illidan had gained a significant upgrade from Kil'Jaeden, and Arthus was only back to his old self because the LichKing used much of his power to get him back to normal capacity.
Also I would like to state another point that in the Manual of Monster Illidan is far from as strong as the Artha/lichking fusion, but Arthus alone based on previous states is i we follow that line no match for Illidan.
Originally posted by Burning thought
ime not sure about this book, whats its accuracy like, its date of publish and such? wheres it come from, is it canon?
2003 and there isn't a lot that has changed in that time in regards to Arthas and Illidan besides the fact that he later has gone insane.
Canon , Indeed. It's this book