One thing the sequel trilogy lacked was originality. Even the biggest defenders of Episodes VII-IX can’t deny the films relied heavily on nostalgia and offered very few original or new ideas to the Star Wars galaxy.
While Starkiller Base certainly wasn’t an original concept, it was executed in an original way. A planet-destroying weapon is definitely not anything new in the world of Star Wars. We obviously have not just the Death Star in A New Hope but a second Death Star being constructed during the time of Return of the Jedi.
Now Starkiller Base isn’t just a planet-destroying ship, it can take out an entire system of planets. That isn’t necessarily an original thought as more of just an upgrade of the power of the Death Star, but the concept of this ship, if you can even call it that, is something that was an inspired idea.
Starkiller Base isn’t a man-made space station like the Death Star. It is actually made out of the planet Ilum as the Empire/First Order carved out its core, turning the planet itself into a superweapon. The idea of turning a planet into a weapon is a cool idea, and it makes Starkiller Base one of the more unique “ships” in all the sequels.