It's a big eureka moment, and then the film ends, like all movies should, with Emily Blunt cocking a shotgun. And don't get me wrong, A Quiet Place is a good movie, and I never would've suspected that the dude who made a name for himself by hazing Dwight Schrute could direct a hell of a suspense sequence. It's just weird that all of the world's militaries, experts, and random citizens had previously failed to come up with this within hours of the monsters turning up. Even if the initial invasion force included a weapon that lowered everyone's IQ by 20 points, wouldn't someone have stumbled across the solution on accident before then? The world is full of obnoxious loud noises!
But even worse, in almost every case, the "too easy" resolution diminishes both the story and the characters. Every one of these movies -- including A Quiet Place -- involve a whole bunch of selfless good guy deaths on the way to victory. Those sacrifices look pointless once the enemy is revealed to be a sad paper tiger.