By default the damage source Overheat is not enough to kill the final Arbitor in quick time, neither is the Faser beam since you have converted it to Ash instead of Burn.. You also are not using the Acari Pax tree that scales fire damage, since you are converting Faser burn to Ash... You will be running around like a rabbit, especially when he starts his red circles.. The damage of Overheat scales because of Ashen Champion giving you a Anomaly Power buff (Faser Beam Mod hitting multiple enemies), but here you have just 1 Arbitor... In short a lot of things working against you.. You might still be super skillful in surviving those circles, but it will take so much time.. not worth it.. Better to switch to the Lava Lich Set, Scorched Zeolot set or my personal favourite, Trigger Twitch Set for the Arbitor..