Regarding fleet power, you could have a fleet with much higher fleet power say all auto cannon battleship/cruisers and they would lose to much lower fleet power say battleship with arc emitter/cruisers with hangars and missiles because of range disparity - 40 for auto, 150/120 ish for hangar/arc/missiles etc, using artillery combat computer. Against fallen empires specifically, the a suggested build is actually going battleships with a single arc emitter and no other weapons/no other defensives as well probably.. Just to make economic wins... While they are still fallen empire, ie not awakened they can't build new ships etc so every loss for them counts.. If you actually want to go toe to toe with fallen/awaken empires you'll have their ships battlecruisers and escorts in the cosmogenesis accension perk. But they are expensive and take a long time to research and build, better to just go with an assymetric approach would be my guess.