yeah.. German Shepherds are great example,
The real good ones do not have that dysplasia that we pushed on them for the Contests.. 
The bad ones are the winners.. Go figure.. 
My last one was a recue and not pure. She lived to aprox 15 years old.. Pure ones are lucky to live half of that with quality time

Yes, the quality of the breeding is a huge issue. There are some breeds that have breeders who breed for utility, the dog's working ability. For example, some Eastern European German Shephard breeders. The dogs are not bred for conformity or appearance, so they wouldn't win any bullshit dog shows, but they are athletic and healthy.

siggy47

Dogs_And_Cats

Are Mutts Healthier Than Purebreds?

the more pure, less the genetic diversity. My pure dogs lasted way less then crossed breeds.. 
Also, the way people breed dogs is not good.. They go for volume instead of quality and end up messing up..