...the two great Numenoreans, Aragorn and Faramir, are the two leaders of the respective groups. I think Tolkien just liked the idea that great leaders could operate with subtlety and stealth, not just in open battle.

In my, very humble, opinion, I thought Denethor read a lot between the lines in his talks with Pippin, so Pip could have let it slip somewhere.

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Those who used the Nine Rings became mighty in their day, kings, sorcerors and warriors of old. They obtained glory and great wealth, yet it turned to their undoing. They had, as it seemed, unending life, yet life became unendurable to them. They could see things in worlds invisible to mortal men, but too often they beheld only the phantoms and delusions of Sauron. And one by one, they fell under the thraldom of the ring that they bore, and under the domination of the One. And they became for ever invisible, save to him that wore the Ruling Ring, and they entered into the realm of shadows...