So the question isn't whether WoW is too easy, it's whether that's a bad thing or not. Does it matter that anyone with enough time on their hands can become a raider? Does it matter that anyone, from child to grandparent, can pick up the game and find something to do?
It matters to Blizzard, of course-- WoW's low threshold for involvement is one of the reasons it's done so well. You don't need the reflexes of an FPS gamer or the cunning of a master strategist to get to level 70. But to players, the difficulty of the game overall shouldn't matter. WoW is easy, but Blizzard has gone out of their way to create parts of it that are not-- winning in the Arenas is definitely not easy. And though better gear makes many endgame fights easier, I'd guess that no one would argue against the assertion that endgame fights are getting harder in terms of strategy all the time (sure, like any good puzzle, once you figure it out, it's easy, but figuring it out as a guild is not necessarily an easy task).
There are parts of WoW that don't challenge people who've been gaming for a long time, yes, but there are many other parts that do. The question isn't as simple as whether WoW is too easy or not-- it's more a question of, easy or hard, whether the game is compelling enough to keep you interested.