So, in one of my earliest playtesting games, I had a guy playing a dude in a trenchcoat who was cagey and didn't talk much. You'd think this was a stereotype, right?
Well, he had some reasons for being that way. Maybe it was the fact that he had a talking ancient mask stashed in his (enchanted) overcoat that was the source of much of his power. And that mask insisted on staying hidden whenever other ancient (or not so ancient) powers stood nearby. (Another player's theory about that mask is what lead to the notion of an Autumn Court that crept into the book's text just a little.)
And he also wasn't going the loner route. As I recall, he was a bodyguard by trade, and that had bound him closely to the other PCs. He might be a very private person, but he had plenty of reason to hang around other people, to be part of a group -- even if it was "just a job". (Or was it? His mask's attitude towards the work he did was unusually encouraging.)
So, this is something I wanted to point out because I think it breaks the loner paradigm neatly and clearly. Loners, for me, are people who actively work against being a part of the group.
I don't think Thomas qualifies, there. Family is important to him, whether we're talking about his brother or his sister. He's a joiner. He might have lots of reasons to lie, to put off airs like he doesn't care, but he does.
As to "I'm evil but not really" side of things: I think the other posters have got it right. There are very few examples of unalloyed goodness in the Dresdenverse. So that's not an escapable paradigm. We can't all be Michael -- nor should we. If Michael Carpenters were frequent, they wouldn't stand out as such an important, vital part of the mortal struggle against the supernatural.