It isn't OP if the requirements for the gun are for the Titan to run Armor of Light like Immobius requires. This way, the Titan can't cheese with Weapons of Light behind projectile shield for ~30 seconds. It simply becomes a normal AR encounter with a brief bonus of deflecting incoming enemy fire - the enemy can always leave the Titan alone. Honestly, if you are engaging a Titan sitting in his/her bubble, you're asking for trouble...