Like you said, it's layered
. I think Ichikawa would be a bad writer if she didn't write being trapped inside of another person his entire life into his character, and I don't think she's a bad writer. Even say Ghost was 1000 years old, Cairngorm didn't seem to come out or have any real influence most of the time, so he probably only really "lived" for about 50-100 years total, but even then, you can't get much experience as a person by desperately, constantly lashing your way to the surface of consciousness and apparently usually failing.
Basically, Ghost had another person, apparently someone about as emotionally mature as NuMorga/NuGoshe, trapped in his head that he could feel and talk to with his thoughts, yet actively suppressed his existence. I don't think Ghost was a good person.