[@Lmpkio]
Even Darth Vader crushed a Star Destroyer once. That's like, Sith Lord entry level. Darth Sidius was so powerful his voice had enough power to kill people. Darth Naga Sadow once created a Supernova, using the force to explodify a STAR. Darth Tenebrae wiped out the life of entire planet and absorbed their life force in a single force attack. Luke was able to destroy an army of over 10.000 drones with a single swing of his lightsaber (not a Sith, but uses the Dark Side, so technically counts). Darth Revan was able to fight Darth Tenebrae and live (and considering this man one-shot an entire council of Sith Lords with ease, that's a feat). Exar Kun was so powerful, it took an army of thousands of Jedi in order to stop him, and the best they managed is to imprison him.

Starkiller is a meh Sith. He's decent. Knows what he's doing, can point a saber in the right direction. But on the Sith Lord scale? He's pretty much at the bottom.