Michael Martinez has a long essay on balrogs, and if Aragorn and Boromir could have helped Gandalf fight Fred the Balrog on the bridge in Kazadum.
the essay is a long discussion of what is a Balrog, and how the concept of Balrog changed in the 50 years when Tolkien was writing his tales.
But essentially a Balrog is a fallen angel of the Maiar class who has taken a bodily presence in Middle Earth. And it is doubtful that human heroes, even one with elven/maiar ancestors like Aragorn, could have stood out long against Fred the Balrog of Moria.
Fred? Yes, that's what the fans named him sort of a jest, in the same way that the Great White Shark in Jaws was named Bruce. (or in the modern world, Hitler was Herr Shickelgruber and Xi is Winnie the Pooh).
Because laughing at the devil really really makes him mad,
and the warrior of legends of east and west jest as they fight evil, knowing that they will probably be defeated or at best win a battle that will only be a temporary victory in the long defeat of history.
But they chose to fight nevertheless...
Tolkien's theme of the long defeat is a variation of the Northern myths, where even the gods know that at the end of time, the Giants will destroy Asgard and the world, but they will oppose the evil anyway, joined with the warriors of Valhalla.
But one difference between Tolkien's world view and the world view of the Northern myths: in his worldview there is hope that good will conquer in the end.
Tolkien had two words for hope: One was the same as our idea (short term hope that things will go well). But the other term he uses is Estel: This is the long view of history, the hope that assures us that in the end God wins: that after the death on Good Friday comes the resurrection. And after Armageddon comes the New Jerusalem at world's end:
He will dwell with them, and they will be his people, and God himself will be with them as their God. He will wipe away every tear from their eyes, and death shall be no more, neither shall there be mourning, nor crying, nor pain anymore, for the former things have passed away.”