A good counterpoint to the idea that most purebred dogs have health issues are gundog breeds that are still judged based on hunting and retrieving field trials, or other dogs with real jobs like police/military dogs, herding dogs, etc.
Athletic breeds with real jobs typically have much longer life spans. Even AKC Border Collies and German Shorthaired Pointers have average lifespans of 12-15 years, with it not unusual to see dogs that are 16-18 years old and still healthy. My own dog is a GSP, and I not only met his father and mother but also his grandmother, who was perfectly healthy.
German Shepherds were epically screwed up as a breed in the 20th century by intentionally breeding heavier dogs with unhealthy body structures that looked aesthetically pleasing. This is a big part of why Belgian Shepherds (Malinois) replaced GSDs and Dobermanns as military and police dogs in many countries. The extreme form of this aesthetics problem is the French Bulldog, which is an abomination that shouldn’t exist according to the laws of nature, because it typically can’t reproduce without caesarians and/or artificial insemination.