User blog comment:ChishioKunrin/What Chapter 12: Breach Needed/@comment-11188061-20141106062626/@comment-9090085-20141107074726

Pretty much. The walls of the kingdoms have kept the Grimm out for hundreds of years at least, considering they were able to have a few wars without the Grimm breaking in and killing everyone. Plus, the Nevermore isn't some new Grimm that's appeared recently; it's a "design" likely older then the walls; so it would be ridiculous that there's no defense against them, especially in this age of technology Remnant is in(even the "baby" Nevermores that attacked Yang came out of the hole).

Gun encampments maned 24/7 combined with patrols by Hunters and Gunships would be more then enough to keep Nevermores from entering the city.

No mater how you look at it, Coco effortlessly killing 4 giant Grimm shouldn't have happened this episode; not just because it robs those Grimm of their threat for a volume finale, but because Grimm of that size couldn't have gotten to the fight to begin with.