Through out the 61 yard range, the feather fletched arrow arrived at each distance in less time than the vane fletched arrow. When the arrows yaws, this added grip helps realign it quickly and efficiently. The huge weight saving with feathers also helps stability. Add too much weight on the rear and the arrow will try to swap ends. Finally, as the fletching crosses the arrow rest on release, feathers simply fold down out of the way, then pop back up.
Plastic vanes bounce the rear of the arrow far out of alignment.
While the arrow is yawed, aerodynamic forces are forcing it AWAY from its original path. The arrow is no longer going where it was aimed. Due to the sluggish straightening ability of plastic vanes, the arrow typically oscillates from one yawed condition to another. This yawing cost speed, range and accuracy. What's more, the penetration upon impact of a yawed arrow is lower than an arrow flying straight.