We have to start by assuming that the naked classes are balanced. If not, that's a whole separate issue. Warlocks do not really have a perk that gives them two grenades. But to the extent that it is true, we must assume that this is balanced e.g. by a lock's lower resistance to damage. So, now this all comes down to gear. There is nothing available to a warlock that is as good as that titan chest piece. The classes are balanced, apart from armour.