It is. A surprising amount of Forerunner technology is made up of energy and hard light. Especially so for Forerunner starships. They are actually held together by hard light bonds, not by super-rivets or metal. With the Composer, it requires a massive amount of tuning and power to operate in the way the Didact wanted to. So when the Chief destroyed the Composer with a nuke, it severely disrupted the energy flow and distribution, so the command module of the Mantle's Approach lost primary structural control, and as a result, the ship fell apart.