The "joke", of course, is that he's actually just a broadly heroic character who serves to bring the average morality of his group up (well, especially by counterbalancing Tabitha) and the fact that he tends to get the credit and is the face of the group isn't something he deliberately does it. It's just that he's likeable, handsome, and good at talking to people.
To put it another way, "everyone is just Evil really" is boring. Guiche, Kirche and Monmon are all broadly heroic, and Tabitha is the party's antihero. If everyone's a bad guy for realz, then it just turns into a dark mire and then you stub your toe because you can't see where you're going. And of course, I'm doing a pastiche of fantasy, and that means that the small band of heroes actually have to be heroes. And also, yes, killing machines who can blenderise their way through vast swathes of bad guys. Fantasy pastiche, after all.