from the years I have been in the dogs there is one thing that drives me in breedings I make and that is consistency
the only way to get consistency for high ability is to breed only to those animals
if you constantly weed out those that are not able to win shows , the percentages get higher
There will always be exceptions to the rules and people tend to look at those exceptions to justify their particular breeding
but every working breed as far as I know uses the same rule