Even though Valandil didn't claim Gondor all those centuries earlier, Elendil's own line carries the senior claim to the High Kingship of both Arnor and Gondor. Aragorn, as the direct descendant ...

But we were all of us deceived, for another heir of Elendil (Peter McKenzie) was made. The prologue doesn't show it, likely because of narrative or time constraints, but Isildur had a brother ...