[William Cloud Hicklin]

I was thinking more of Denethor's reaction if Boromir had indeed returned to tell how no one would accompany him on his journey back. That wouldn't have done much to elevate Denethor's considerations of other potential allies in the West.

But Boromir wasn't sent to seek allies, but to seek the answer to the dream-riddle. That he certainly found.

WRT another line of discusion: although Bormir certainly learned right off the bat who Aragorn was, that "Who" was "heir to the North-kingdom, Chieftain of the Dunedain of Arnor." That in itself did not imply advancing a claim to the throne of Gondor; a thousand years' worth of Aragorn's predecessors had not done so, even though some of them were certainly in communication with Minas Tirith from time to time. Boromir plainly had no problem with the idea of Aragorn coming to MT, seeing the Sword (and possibly the arm that wielded it) as great potential help in the war.