First, the wiki means nothing. As a member of the wiki I can confirm that it is nothing but a public blog. Unless the statement is backed up by canon evidence, then it is worthless.
Second, "feudal monarchy" doesn't describe how the monarchy comes to power. It just describes the direction of rule. One or two monarchs, sole or joint-rule, commanding over lesser nobles in a feudal setting. That's all that means.
Second, the actual video games confirms that the monarch's power derives from the banns. So the banns elect the monarchs. The throne does not pass through the bloodstream. Being of the blood simply makes you an eligible candidate for it.
Now, regarding rank, yes being a teyrn gives you an edge in terms of strength of your claim. Arls serve under teyrns. That's a fact.
I agree that being a teyrn does not automatically make you the king. All I'm saying is that being the highest ranking teyrn while there is no monarch makes you the highest ranking figure of authority. That doesn't make you king, but it makes you a strong candidate for the throne, to be decided by the banns.
Royal blood or relation to it by law does not give an upper hand except with banns who cherish such things. As we see in the game, blood relation means diddlysquat to the great majority of banns. Regarding those banns, I would think Alistair would be favored over Anora since he at least is the son of Maric, though not Rowan. But would they rather have a half-blood Theirin or a full-blood Cousland? I'm sure most would choose the half-blood Theirin, but my point is that this fractions the fraction of those banns who consider bloodline to be important. And don't forget what Dairren said. Many thought Bryce should have been king instead of Cailan. Which means there are banns who favor the Cousland bloodline even over a full-blood Theirin. Granted, these may fall in the category of those who don't care about bloodline, but some might be in the "bloodline is important" camp.
Fergus abdicates by default when he is injured in the Korkari Wilds and takes a year to recover in a Chasind hut. He's M.I.A. and presumed K.I.A. There was no way he could fulfill the duties of Teyrn of Highever.
Please provide proof that the eldest of the teyrn/teyrna inherits the title if no heir is named.
Grey Wardens can hold titles, especially if the Warden in question rejects what the Wardens stand for, like my male Cousland did. Oh, and like how Alistair can.
A claim just means you're an eligible candidate. The Cousland has a claim through title and law. The banns would have no problem with the Cousland being the sole ruler. It is legal and the most practical option, unless that particular Cousland is a complete moron or something.
Whether or not the title makes the Cousland more suitable is a matter for the banns to decide. I think it does over Alistair and Anora, but the point is that the title makes you an eligible candidate for the throne.
The "rightful heirs" are Alistair, who is loyal to the Warden by default, and Anora who is the daughter of a traitor and king-killer. And remember, Anora had no allies. Only her father had allies. So basically it comes down to the Cousland vs. Anora. And when I write "Anora" I mean Anora by herself. The Warden has the Circle, Ferelden forces, and possibly werewolves who will be happy to kill anything you turn them against. So yeah, you tell me who wins that one.
Actually, the terms of the duel were that the banns would abide by the decision. So the duel itself would compel the banns to honor your self-appointment. As Arl Wulf can say at the Landsmeet, how do you think Calanhad took the throne? He presented himself before the Landsmeet and declared himself king. All banns bowed to him, and funny thing is, he too had mages at his side for that. So yes, the fact you win the duel compels all banns to obey your decision.
He declared himself regent, and Anora had no ruling authority. She was a consort. A regent is not a king. Loghain was acting as regent before the Landsmeet. When Eamon called the Landsmeet Loghain put himself forward as king. Anora had nothing to do with it at that point.