Hunters make their own armor, generally by integrating bits of Titan and Warlock armor together along with whatever they feel they need. Warlock armor is focused on freedom of movement and assisting their mental capabilities. Their abilities are dependent on them maintaining Flow State, a real psychological/physiological phenomenon (google it, pretty awesome). Because of the need of freedom of movement, it actually relies more on the technological side of the armor than the other two, so heavy armor plates aren't needed.