It’s not an awful conceit, but…
…if a bunch of plucky protagonists can make it from Point A to Point B with nothing but their wits and a little kinetic energy, then the goram USAF could have pushed the damn monsters back with a whole lot of kinetic energy, in the form of a bunch of A-10 Warthogs and their Happy Mandatory Fun Time GAU-Avenger rotary cannons. I mean: how could depleted uranium rounds do any worse than arrows, in this situation?
Oh, well, they’ll probably explain it away at some point.