Its because luke wasn't shown to be a jedi, all you saw from him in the movies was basic lightsaber fights. In the novel he is potrayed more but its not as much as a wow factor because you don't see what it would look like on a game or a movie, etc.
Starkiller though is however, much more then Luke.
Taking a destroyer down was more then what yoda could do when Yoda was facing the Emperor. =P Then again, do take into fact that yoda was fricken old - still, for an old jedi, he was still better then luke was.
In a 1 on 1 fight, if anakin wasn't in that suit of armor, i still think Galen would beat him.
However, do i think Galen could of went up agains Raven? Thats much much more...debatable, seeing as how the Sith Lords back then =P could destroy planets using the force...