Just as an example. The Eddorians had 2 of their number try to go to Arisia. They passed the screens set up to keep watch. They were taken over by Mentor and rendered insane to the point that they destroyed themselves. The Screens around Eddore are at least as good as the ones around Arisia and are constantly monitored.It These screens block Psy attacks as well as physical attacks. (Blowing up the planet could be a problem for either species) It took the the entire mental power of 2 billion Lensmen backed by all the Arisians, including the CoTL to break through the final screen surrounding the eddorian council chamber. Without all this, the attack on Eddore wouldn't have succeeded. While the Arisians worked on developing Telepathic talents, the Eddorians worked on the Physical side of things. Eddore could not destroy the Arisians with their tech.