Recent revelations have indicated that the consequences of the Order's failure will not be, "Xykon's plan goes off without a hitch and he takes over the world as simply as that." But...

That's not really a change. Until Start of Darkness came out, all we knew was that Xykon had some nefarious plans for a Gate. Start of Darkness gave those of us who read it knowledge of what Redcloak's understanding of "The Plan," which turned out to be the Dark One's plan with nothing directly to do with Xykon, was. I don't know about you, Winter, but I was never inclined to bet a great deal that even Redcloak knew what The Plan truly was. Nor am I inclined, now, to bet a great deal that the Dark One doesn't know what's on the other side of the rifts.

As far as I can tell, your objection is that the Order is not battling a clearly-defined-to-the-audience threat doing something that will have clearly-defined-to-the-audience consequences if not battled. But it's the way it always was, really: The Order battles Xykon to protect the world from the not-yet-revealed-but-safe-to-assume-it's-bad.