As was mentioned, it's all about how well you can tune your set up. Modern bows and archers, be they recurve, longbow, or compound, usually can tune to a higher degree of precison. Even with a large head, 5" parabolic feathers are usually more than enough. Smaller fletchings fly faster though- which is what's wanted with compound bow shooters. Primitive cultures didn't have the time or materials- or need- to tune to the utmost precision or highest speed possible. They made up their arrows knowing that fletchings were simply a necessary part of the equation. If they found the arrow still didn't fly right, they just didn't use it.