The advancement? From what I could gather, think Dark Ages with lots of fantasy creatures and ancient relics.
Instead of having a gun, one of the other archologists could have been a bodyguard instead, and if he/she is the one to deflect, you'd have some tough moments. Think something in rambo style here, so with a couple of bullet chains and a hand grenade or two. That way, you never needed to carry a gun, and the other character just uses it until it runs out and grabs one or two of those chopping knifes they use in the jungle. The problem is effectively solved, since the shooting of the gun is left to someone else and is a regular attack (unless you have complete control over everyone in your party that is. Do you?)
About the traitor, it could also be both, or none, depending on your behaviour in the game and a bit of luck.
And about not being the one, maybe the assistance mode could be unlocked after you've beaten the game. Usually, you are the main character because that's whose part is most interesting, and usually most heroic too.
We're getting back on the right track here. Not depressed anymore
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The last arrow of Legolas kindled in the air as it flew,
and plunged burning into the heart of a great wolf-chieftain.
All the others fled. -J.R.R. Tolkien, The Lord of the Rings
<font size="2">This picture has nothing to do with the other part of my sig. It's just cool</font>