I think you're being too conservative with the anti-aliasing. If it's a long line of pixels being anti-aliased into another long line of pixels, there's going to be a decent length of anti-aliasing pixels of each transition shade. This is most obvious on the clouds and sun, where you just have single pixels of anti-aliasing at the end of long lines.
Speaking of the sun, for something so large and bright in the image, it sure isn't illuminating anything except the sky and pole. That doesn't look right. I'd either cloud over most of it so that the sunlight-breaking-through-clouds-onto-pole was much more obviouis, or illuminate all of the grass not shadowed by the mountains.