Actually, the implausibility of the Reavers being able to pilot spaceships gets to a larger phenomenon in science fiction. From the creatures in the Alien movies to the dinosaurs in Jurassic Park, we're constantly given depictions of ravenous, hyper-kinetic beasts that are simply not in keeping with what we know about biology.
A science fiction version of a lion would be constantly running around, roaring, and tearing apart zebras and Masai tribesman alike. In reality, they spend most of their day resting to conserve energy and are lethargic after a major meal. A harder sci-fi beast should show some of the trade-offs in energy expended versus energy gained that creatures exhibit in the real world. When the Alien leaves Ripley alone we're supposed to be shocked, but in reality, predatory creatures are constantly backing away from potential prey because they're already satiated, looking for a mate, taking care of their young, or have innately determined that the risks outweigh the rewards.
A science fiction version of a lion would be constantly running around, roaring, and tearing apart zebras and Masai tribesman alike. In reality, they spend most of their day resting to conserve energy and are lethargic after a major meal. A harder sci-fi beast should show some of the trade-offs in energy expended versus energy gained that creatures exhibit in the real world. When the Alien leaves Ripley alone we're supposed to be shocked, but in reality, predatory creatures are constantly backing away from potential prey because they're already satiated, looking for a mate, taking care of their young, or have innately determined that the risks outweigh the rewards.