It seems the best possible flight arrow would be made of the densest material available having needed stiffness and elasticity. Greater density allows reduced wind resistance, the main enemy of flight arrows.
Copper is about 7 times denser than the densest wood or wood-like material, and can be primitively processed to have varying properties friendly to flight arrows.
Copper was processed into artifacts around 7k years ago, a couple of thousand years before animal glue was processed.
If a bow made with hide glue is a natural-materials object, wouldn't an arrow made of copper also be?
From a only-natural-materials position, if it's wrong to use copper it's wrong to use hide glue. Can a facts and logic case be made against that claim?
Osmium arrows, SG=22, are obviously out, osmium processing requiring post-primitive cultures. But why not primitively processed copper?