Aragorn as Thorongil

So I thought Aragorn's role as Thorongil is super interesting. He aided his true kingdom under a pseudonym so as to protect his identity and not cause any strife for the steward Ecthelion. And the fact that he had once before looked to the Corsairs of Umbar and defeated them so as to protect Minas Tirith is definite foreshadowing to the War of the Ring. What do you guys think of the hypothesizing that one of the reasons Denethor didn't like Mithrandir was because Denethor viewed the wizard as conspiring to supplant him? What right does Denethor have to stand in the way of the return of the true king? But to play the devil's advocate...how easy would it be to give up ruling a city after the Stewards have watched over said city for hundreds of years?