Board Thread:Suggestions forum/@comment-26429944-20180208085334/@comment-26298013-20180213231438

But their kingship is, in fact, based on their LORDSHIP on Numenor, which was because of their ties to the royal family. As in, Elendil is the King of the Faithful because he was a cousin of the king, and thus was royalty. Elrond, however, is (possibly) a level of royalty above him, being the eldest of the ruling house, even if not actually in the direct line of succession.

But again, it cannot really be proven one way or another, so I stick to the opinion that being able to call Elrond the rightful King of the West is pretty darn cool.