The combination of having Stealth and Backstab is what makes rogues deadly. Also, Fear and Death Coil suck from diminishing returns.
Death Coil is on a seperate immunity timer, and since it has a 2 minute cooldown, you'll never have to worry about diminishing returns. All you have to do when you're dueling a rogue is hop around pressing the target and death coil keys. When it hits him, you run back a bit, fear him, cast dots and keep fear on for as long as possible. When it's no longer a possibility, you just run around so he can't get to you. Warlocks are overpowered one on one, but a good Rogue still stands a damn good chance.
In addition, stuns have diminishing returns. To stun lock a Warlock, I'd generally do this:
Cheap Shot (2 combo points, 4 seconds)
A few sinister strikes (Two, for an additional 2 combo points)
Gouge (another combo point, 4 second stun)
Kidney Punch (6 seconds with the 5 combo points obtained)
Sinister Strike until you're dead.
I'm a sword Rogue, which means I don't use backstab. It's a disadvantage when fighting clothies, but it makes me much more versatile in both PvE and PvP (in most cases, anyway).
I'm fairly confident I could beat a same-level Rogue on my Warlock once I got back in the swing. ( My Warlock is level 51 ).