Maybe since the Nebari weren't given a role to play in the end of the story, you could say that the Nebaris and Eidolons are examples of, respectively, the wrong and right way to go about doing the same thing. Perhaps the Nebaris were directly inspired by the Eidolons, but instead of coaxing out the essential reason within people, chose an alternate, more forceful route. Also, Eidolon presence is required to maintain their influence, whereas what the Nebaris do is supposedly permanent, closer to a lobotomy.

A link maybe could be drawn with how the Peacekeepers developed from people who could bear their name unironically to their current, almost Fascist state, and how the Nebaris also took an Eidolon idea and perverted it.