The parallel between the possessions of Golbez and Edea is fairly clear to me. I think that it just depends on how you view possession, because I consider a person being heavily influenced into doing the bidding of another pretty much the same as someone actually occupying the body of another because of the end result.

Final Fantasy IV: The After Years allows you to see more into what happened to Golbez. He clearly regrets all of his actions, but it is clear to me that the person who committed the atrocities in Final Fantasy IV is not the same person who becomes a playable character in the sequel. It is really hard to say what, exactly, happened to Golbez as he was taken by Zemus at such a young age. I reckon based on his loyalty to the Lunarians that he feels like he cannot go back to the human world because he has only brought darkness to it.