Obviously it doesn't affect a horse if you breed back to the same stud and it's a good match. But several top KNN breeders just Svened their top girls to National Treasure and then his descendants (also Scp weak ) and hoped for the best. The current #1 KNN (weakest in Scp, has got to have Nate in there 30+ times.
I think it would be a fun stat to add. I assume most serious players won't let it change a horses worth so I don't imagine it will affect the game that much
It does when it perpetuates certain weaknesses. For a while, the only WWW KNN boy was National Treasure, who was weak in Scp. Everyone bred to him, and a large portion of EEE+ KNN are still Scp weak.
Myth in my experience it's only EEE+ KNN that are 'weak' because they're been inbred to the point that certain weaknesses are crippling them. Most PPP-EEP KNN, which it looks like they're using, are equivalent to those of other breeds.