the spartan laser was the most advanced weapon, the war was recorcse heavy. Not enough time and matireis to do so. (please excuse spelling errors.)The MAC was the most effective anti-ship weapon in the UNSC arsenal, capable of destroying any other human ship in one shot. The Covenant's plasma torpedoes were very effective as well, but the UNSC could not get close and examine one to reverse engineer it, so they stuck with the MAC gun. Instead of changing weapons, they strengthened the MAC and began putting multiple guns on single ships, such as the Destroyers.