And Guardian armor looks like robes and football gear, but it's actually a combination of micro-servos, plasteel, and neurological interfaces. Also, we have no idea how Eridian Tech and Light tech interact with each other. That said even if they are on-par, the Hive and the Vex are the clincher here, not the light. The vex travel through time and turn entire planets into chronic dimensional network nodes, and the Hive we able to, somehow, drain energy from the Traveler a while being on a completely different celestial body. Eridium mutates things. Light, Darkness, the Vile Energy of the hive, the Ether of the Fallen... they do something else.