The only thing wrong with Campbells' idea is that in so many myths, the hero is overshadowed by fate or destiny. So many have a prophesied death and, despite all their efforts, fail to avoid it.

You mention Mount Doom, but who is the hero there? Frodo, pawn of destiny, trying at the last to overcome his fate? Sam, who followed his master out of duty and loyalty, but ultimately by his own free will? Or poor, thrice-cursed Smeagol, who takes the burden from Frodo and dies fulfilling anothers' task?

We are not so much the hero of our own story as the protagonist. But the test is really to see if we can become the author.