I think Kyurem is more energi-less, as things without energy is cold and it looks rather dead/weakened. Like if it's energi was splitted between Zekrom and Reshiram, and Kyurem is just an empty shed.I've always felt Reshiram and Zekrom represent the energies of the world.
The warm and life-giving energy of fire, the fiery, destructive energy of thunder.
Kyurem would represent the freezing and eternal energy of ice.