Regardless of what you may have been told, heavy arrows are nearly always a better choice for traditional archers who shoot traditional bows. Traditional archery is about accuracy, predictability, and control.
Because the grain of a bamboo arrow runs differently from other wooden arrows, and because bamboo comes in many grades of quality, it takes a bit of knowledge to properly measure the static spine of a bamboo arrow.
In the centuries before high speed film, it was clear to archers that an arrow didn’t necessarily fly where it was pointing. This paradox, which became known as the “ARCHER’S PARADOX”, was the name often used for something which shouldn’t be happening…BUT WAS happening. High speed film cleared up the matter. Now we know that not only is an arrow flexing and spinning as it launches into flight, but the line of the flight can actually be bent as well.