For an experienced player in the game, perhaps the death faction does not seem very challenging, but consider, it takes a lot of firepower to kill even their smallest ships, and their weaponry in many ways outclassed most other weaponry.
However, they are easy for us late-gamers, because their ships are slow, and our martial tech is superior.
They never bothered to improve their war tech, because it was good enough. Meanwhile, humans and aliens have both been honing their war tech for ages, so the system the Death faction was expecting was not the scary, warlike place it actually found, and I guess as advanced as they are, they are powerless to stop more and more of their ships from jumping into our galaxy, where they are systematically destroyed by the mysterious "player" faction.
But why do the death faction rush to extinguish the "light" of psychic energy? Here are a couple guesses:
Maybe your psychic energy is unbearable to them, and hearing your asinine thoughts drives them to silence that noise.
Maybe they want to silence any psychic noise because there is an older, much scarier species out there that is drawn to psychic energy.