If you want to make hexaguns useful, the simplest way is to make them the opposite of what they are now. Make them more powerful, but slower than normal guns. Melee cors hate hexaguns because they get less damage and less TP return out of their WS, not to mention the nerfed quickdraw damage. Range cors hate hexaguns because they do horrible damage and eat ammo like Yilbegan eats Tarutaru. So just make a hexagun with 90 base damage and 900 delay.