Darth nihilus was in fact capable of using his unique ability from a star system away. It's true though that he was within orbit of the planet that he consumed. You failed to mention force storms. They have the potential to tear the fabric of space time and reality. It can be used in many ways but its essentially a wormhole on demand. Aside from obvious force related strengths star wars is home to some of the most terrifying weapons known to the science fiction world. Devices that can theoretically destroy the universe via hyperspace collisions. Other notable weapons could in fact desimate solar systems and planetary destruction is quite a common feature amongst super weapons in star wars.