People who are hardcore defenders of either game are, for lack of a better word, retarded. Despite what WoW has become, the fact remains that it did many things right, for however long that may have been. If you can't see or admit this, you're beyond help. In this industry, if you can't learn from the past, whether it be your own or others, then you won't succeed. It would be absolutely moronic for any MMO developer NOT to take certain things from WoW, as well as many other games. The way to greater success is to improve upon what has already been proven successful.
WoW has been turned into a casual-friendly borefest for anyone who wants an actual challenge. If you consider yourself a gamer and not a casual, then you will likely enjoy Aion more. Trying to determine whether Aion or WoW is "better" is dependent on many things. If you're talking about profit, then Aion will most likely never surpass WoW, because WoW caters to an incredibly wide audience (read: casuals), while Aion aims to be more of a hardcore gamer's game. If you are a part of Aion's targeted audience, then you will find Aion's gameplay to be more rewarding. Its as simple as that. Trying to argue one way or the other is idiotic and frankly, a waste of everyone's time.