Gondor’s own laws and rulers even recognized how ridiculous Aragorn’s claim was. Arvedui, the last king of Arnor before he drowned in a shipwreck, once claimed the throne of Gondor, but the Council of Gondor rightly rejected him, saying the royal line of Gondor was descended from Anárion, not Isildur. Aragorn, like a many an illegitimate dictator before him, was only able to seize power due to the breakdown of law and society during the great crisis of the War of the Ring. Even then, with the doom of Gondor looming, Denethor the Steward of Gondor told Gandalf he wouldn’t bow to Aragorn, “last of a ragged house long bereft of lordship and dignity.” (Denethor may have been Middle-earth’s Worst Dad Ever, but he had a point there: Aragorn came from royal stock, but the only thing his family had administered for a thousand years was a forlorn wilderness full of ruins, wolves, and trolls that talked like Victorian gutter urchins.)
This is, of course the claim of monarchial legitimists, who seem to think that monarchy depends upon nothing but descent. They miss the key point, that monarchy depends upon descent from divinely-favored persons. Monarchy is sacral. Always has been, always will be.