I think it's intentional that we don't get to know Connor while he is alive. I think the point is that whatever he was going through inside, no one knew the extent of it, and he couldn't connect with anyone. If they had shown more of him, I think t would've lost some of that.
And as to the behavior of his "ghost," the reason it was out of character for him is that it wasn't Connor's ghost. It was Evan imagining talking to Connor and projecting his feelings. Evan was talking to himself, but imagined he was talking to Connor. That was my initial interpretation, but at the talkback on Sunday, Michael Grieff alluded to it as well, because he said something like "when Evan was talking to himself, or rather projecting what he was feeling onto his imaginary conversation with Connor..."
So after Connor's death the authors aren't using him to develop his character, they're developing Evan and his internal dialogue. Connor's "ghost" cares so much about Connor's parents because Evan does. And Connor seems conflicted about what Evan is doing, because Evan is conflicted. Sometimes he uses the projection of Connor to justify his actions, and sometimes he uses it to try to get himself to stop.