I used to think that but my experience has not born that out no matter how carefull I checked the breeding records.
I have two purebread goldens from the same breeder. Both have immaculant breeding from champion bloodlines. One is the best dog in the world. The other has epilepsy and ear problems. The sick dog costs 120.oo per month in medication and he still has horible sezures once in a while.
We've had two other purebreds and the health ratio seems to be about 50 percent no matter how well we check the breeding. We have never had a problem with the muts?
I agree with the logic of your statements and I agree that it should be true, my experiences don't support it.