Well Bred vs Backyard Bred - Page 11

Here is where you're wrong. There have either always been underlying health problems or there haven't been; genetic flaws to not spontaneously generate themselves. If a group of dogs has no genes for a given trait, that trait will never appear (except for possibly in the case of a chromosome anomaly which would be limited to the individual) despite how closely they are inbred or line bred, how often or for how long.

you are correct to a degree. but if you look a hounds for example. years ago  (still some today but not as prevalent)
many of the hunters did not have the money or the means of travel to seek outside there lines. They were heavily inbred for generations. The litter size decreased and had many many cull dogs. The pups kept alive were selected ruthlessly. and i mean ruthlessly as the rest were killed.the ones kept may be 1 dog out of a littler of three. or the one pup litter had been killed do to insufficiently in that one dog. When you breed that close you either come up with a cull dogs or a super dog so to speak. If you want to learn about close line and inbreeding study the old hounds. It was done religiously. The flawed traits will be brought out much more significantly in a high percentage of dogs. 

there was a very limited gene pool to begin with which isn't the case

All purebreds are a closed gene pool. Simple fact. I don't care if you breed a million pups. The gene pool is still closed and originated from the original 12.dogs. So the dogs are inbreed and closely line bred to create the pure breed. Thats why we have specific genetic issues tied to breeds. Dogs dying younger, diminished immune systems, bloat, HD, ED, etc....

When you create an off shoot to that you close off another circle to take a portion of the original gene pool. You once again have to take the same road  and compound upon those issues. The dogs aren't selected for breeding/ living as ruthlessly as the hounds were back the in the example above so you create a week pool. So without the selection process being all inclusive and stricken down it is destined to fail.

This is why in just working lines you see your old ddr, czech, east ger, west ger,and all of these lines. the all hold different traits as the pool was closed for years. Now you have people who cross them to end up with the dogs they want to blend the traits. However in the working lines the lines were more selectively approached to maintain the ability of the dogs as well as some conformation because they needed them for police and miltary(due to wars) and couldnt afford to loose there durability.

Show gets a bad rep as now the fads of confirmation of show dogs in general creates it own breeding problem. You problems also come from negligent breeders who do breed for only the listed traits need for a good paper dog to make money(not that others dont). Therefore not being as ruthlessly selective in the breeding's of that second closed pool you will become haunted with a great many issues. Along with the changes in angulation, structure, stride and power will put the show line at a disadvantage in some tasks agreed? now we have said there are diamonds in the ruff. and anyone who has worked dogs knows heart in a dog can overcompensate for a lot. But the changes made due to fads, and the vast majority of wrongful breeding's has and will continue to lead to your demise.