I'm astounded by your aggressive defense of the game's characters and lore, which themselves are absolute weaksauce and defeat the universe's own sense of canon with each turn. You don't HAVE to say anything, and I've got nothing to prove to you. If the basis of your claim is that the name appeared in a game 5 years ago, you're in for a rude awakening. Did Blizzard also coin "Stormrage"? Or "Furion"? Or "Uther"? Two of those are too derivative to be defended as "original", even by you, and the last is from British folklore. So is it that much of a stretch to say that someone, somewhere in the world, might have been "Illidan" before a computer game character? Why don't you track down the 10,000 Harry Potters and give them shit for it, too.
You may have my word that I thought of it before the year 2003, the same way the Egyptians and the Mayans thought up the pyramids independently of the other. That's all I can really do for you. Do I care? Apparently enough to post a quick rebuttal. The Internet is serious business, after all. But do I care what you think? No.