Point taken, however, the army of the Dead was called to fulfill an oath for deserting a
battle, not man-to-man combat. Then too, Arthur could call on Merlin for back-up in which case Aragorn would call on Mithrandir, and then Arthur would call on his knights and Aragorn would call on his army, then Arthur would call on
his army, and it would turn into an enormous battle. The significance about Arthur being the true king is that he was the Pendragon, but the first one after Uther and his heir; Aragorn had to wait quite a few generations to inherit his title and the power that went with it. Then too, Aragorn's bloodline had thinned due to the men of Numenor marrying into lesser races. The significance of this has to do with the swords resonating with the bloodline of their ancestors. Less time of descent, the more powerful the connection would be. Truth be told, I think it would be a very close call, but Arthur would ultimately win because he is the "once and future king" and even if Aragorn managed to mortally wound him he'd just go back to Avalon and wait out the centuries until his return; in the meantime Aragorn would die of old age, unless Arthur had already killed him during the fight. Since we're already talking about Arthurian senarios; what about Aragorn vs. Mordred? (Or Modred, although I've only seen it spelled that way once.)