Here's some more info about the progress in genetic improvements of purebreds that Padgett, among others, apparently advanced by drawing attention to the problems.
Tribute to Prof George Padgett DVM - DogForum.net | Dog Forums and Community
No doubt many took his 1998 offering on purebred dog health problems and ran with it as a reason for advocating for mixes; and then all kinds of good progress took place in purebred breeding and subsequently he published his study findings about mixed breeds being no healthier than purebreds, apparently in a
Dog World article. I can't find the article or his study so far. Interesting reading.