Silent:

A book is a book, and is usually biased in accordance with the writer's personal opinions and experience. I suspect that there are as many books that recommend sharply focusing on the pin.

Although I said that I accept that bow shooters can use either method, and I do; there is a long- established and correct "sight picture," and there are adaptations.

Considering that it is an incontestable fact the sights on a weapon is what actually references the barrel or arrow to the POA and establishes the path that the projectile will follow, I would class the method of focusing on the "spot" to be an adaptation, a sighting method that certain bow shooters successfully use.