Oh, on the contrary, I think the Scoundrel/Guardian is can be very strong. My first character was a 7/13 Scoundrel/Guardian.
What made him really powerful was a combination of (again) the Sneak Attack bonus and Force Jump. When you Force Jump into an enemy, its not able to react, thus you get the bonus. I was taking down Horned Kath Hounds at level 8 with a single hit.