The slope being described is because of angulation in the hind legs of a shepherd. Shepherds have more angulation in the hind legs than most breeds and it's proper that they have more angulation as that's part of why the breed is what it is. The problem comes when people breed for extreme angulation, usually in an attempt to produce a very flowing trot for the show ring. Extreme angulation creates problems.
This angulation is not hip dysplasia, however. There are a lot of breeds that have a much higher percentage of dysplasia problems.
One of the huge mistakes in breeding for a particular look is that any breed bred for looks first will eventually "dummy down" - and our shepherds are no exception. The instincts and intelligence that are typically attributed to the breed are sometimes lacking in this extremely angulated dog .. which, to me, is more of a travesty than the physical appearance.
On the other extreme, you have dogs that are bred strictly for as strong of a drive as possible. These dogs may make wonderful working dogs but generally make lousy pets. They have too much energy and personality for the typical pet owner.
There are many many nice middle-line shepherds, however. People can find whatever they want in the breed for the most part. Just be sure to ask for OFA numbers (not just say "have they been tested?") on sire and dam - both for hips AND elbows - as well as thyroid testing, etc. Ask for health history on the line. If a breeder says "there's been no problems" then I would politely walk away - every line has a problem somewhere and a good breeder will acknowledge that and then explain how they bred away from it.
Meet the dam at the very least, assess her for temperament - and find out how the breeder has handled the puppies for socialization and training from three-eight weeks.
My shepherds have all been healthy overall and they range from full German and Belgian lines to a mix of American and German. None of them are over-angulated.
Melanie and the gang in Alaska