I did come up with a character that has shades of a traitor, only the character would end up being heroic. Basically, he's a sheikah named Nil who starts the game as a rival to Link for two reasons:
1. Nil is trying to earn the redemption of his people by assisting Zelda, but is or at least feels constantly outshone by our green capped protagonist. Thus, he sees Link as an obstacle in his path.
2. Nil envies the Hylians as a whole as they're the ruling race of Hyrule and the ones who kicked the Sheikah out of Hyrule. They live good lives in green fields while Nil's people freeze to death in a snowy wasteland (my hypothesis). This exacerbates his dislike for Link, who is of course Hylian. Nil does make an exception for Zelda though, as she shows understanding and may possibly be part Sheikah (my theory about why Zelda can turn into a Sheikah in
OoT and possibly other games as well as her frequent connections to the shadow folk such as in
TP).
Later in the game, this envy and contempt would tempt Nil to betray his allies, only for him to finally choose loyalty and duty over jealousy and vengeance. So, Nil wouldn't be a traitor per se, but I'd like to think his story at least adds some intrigue to a series normally known for one-layer characters. Whereas Link is ostensibly simple and straightforward, Nil has complex emotions and motivations. And if the current plan for the character seems flawed, he could always be retooled to create a better story.
I agree that the Zelda series could use more complexity in its stories and characters. Just don't go overboard, and certainly don't use contrived plot devices. Mostly, the stories should focus on motivations, preferably strong ones, as well as teach lessons through the character dynamics. The player as Link is able to witness these dynamics and learn and grow from them as a result.