Taulaes

I believe that because Isildur did not make it to take up high kingship, and it says he forsook Gondor, those descended from him only can't really claim Gondor's throne. Arvedui may not have had legal grounds to become King of Gondor, but Firiel and his son Aranarth certainly did. It is true that the law of female succession observed in Numenor was not observed in Gondor, but the reason it was not observed was because it never had to be. Rejecting Firiel because there hasn't been a need for a female to take the throne yet is basically ridiculous. Also, ignoring a law that was in place when Numenor was still around and Elendil was High King was pretty ignorant of them.

No one has mentioned this, but Firiel is directly descended from Anarion, making Aranarth a direct descendant of both Isildur and Anarion, which would re-unite the kingdoms. What makes Aragorn different from Arvedui is that Aragorn is descended from Aranarth, who, as mentioned, is of both lines, so if you really want to get technical, Aragorn *is* Anarion's & Isildur's heir and therefore rightfully ruler of both Gondor and Arnor, the High King. He may have been more acceptable to the people because of circumstances, but he was not just thrown up on the throne because they had no one better.