Luci' bloodline is only thing that can defeat Starscourge/Ardyn, but even they couldn't do it at the start. They needed to pass their power from generation to generation to accumulate it. This also meant that each successor had shorter lifespan because of all the power he held. Until Noctis becomes the destined one, who must finally end Ardyn. After many trials and struggles, partnering with gods/primals, after death of his fiance, he kills Ardyn (he's immortal though), and then he proceeds to use all the power from his predecessors to get into the FFXV's version of lifestream/Aetherial Sea, where he deals final blow, finally killing Ardyn and sacrificing himself. He dies right after, there are no cheap tricks that help him survive, he just fulfills his tragic destiny and sacrificed himself for the greater good.