Something I try to remind myself when writing epic-themed stories — which is a lot, recently — is that my hero doesn’t have to fix The Big World Problem by the time the end credits roll. Rather, he just needs to achieve the small, specific goal I’ve set out for him. He only has to destroy the Death Star.
Yes, that task should be exceedingly difficult. But it’s several orders of magnitude away from The Big World Problem.
Darth Vader and the Empire are still very much kicking at the end of A New Hope. Nazis are alive and well at the end of Raiders, The Guns of Navarone, and every WWII epic you’ve seen. By the end of The Matrix, Neo has learned something of his powers, but the world is largely unchanged.
In fact, the rule seems to be that it’s only at the end of a trilogy that the hero really transforms the world. And you don’t get to make a trilogy unless the first one works. So make the first one at human scale.