Spoiler:
I've dueled him twice now. The first time he ragdolls you with TK after a certain point, but, the Outlander seems pretty confident in their winning. The second time you fight pretty evenly with him but he then knocks you off your feet with TK. He then tries to kill you and HK jumps in the way, blowing up. After that, unless you have Valkorion aid you, Arcann pulls you forward and impales you. With Valkorion's help, you unleash Lightning that causes Arcann to fall down to the city below, however he survives. The Lightning also takes out quite a bit of ships