This is where I don't get culling pups at a really young age, that are bred for sport/performance. By culling say 50% of the litter, you are obviously cutting your chances of breeding from the best pups by 50%, therefore making your original task/goal far longer than it should/would be.
I know many people won't have the time or premises to run on whole litters, but alot of people do and did, and a few people getting together to do so, would greatly reduce the length of time to establish good lines of dogs. A bit like greyhound breeders then maybe?