Mission accomplished indeed. I don't see anyone else defeating the literal essence of darkness and pure evil. Wan, the simple fool, did the best he could at the time. And indeed, he was the beginning of an era: the dawn of the Avatar Cycle. But Korra is the first avatar to undo his grave mistakes. Man's civilization has been brought up nearly cut off from the spiritual side of the world due to Wan's lack of foresight. That wound has festered for ten millennium, until Korra did all that was necessary to make the world whole once more.
Now the universe can go forward in harmony, because Korra deemed it so. All the fallout thereof are the musings and whims of weaker willed people. The Kuvira's and Zaheer's of the world are predictable, yet necessary, eventualities that arise when extreme progress must be made. Does a wound improperly healed not become inflamed, perhaps bleed, when it is properly addressed? These villains are the inherent, weak agents of scabbed blood that must be purged so that true healing and growth can begin anew. And Korra is the arbiter of that cause, in all her glory.