Here's a lengthy article by Benoit Denizet-Lewis on problems with the faddishly-popular English bulldogs (the #1 breed in L.A., a factoid that is cited in the article as a self-evidently alarming statistic).
Back since bull-baiting was outlawed in 1835, English bulldogs have been bred to look like a cartoon of a human baby, with all sorts of unfortunate effects on their health. Back in the bull-baiting days, English bulldogs were vicious beasts, but Victorians quickly bred them for winning personalities. But modern Americans have taken that too far and turned English bulldogs into caricatures of Winston Churchill in senility.
In general, the 19th Century British were just more effectual at dog breeding than are moderns. I strongly doubt that they had better techniques. They just had better goals. For example, the reporter goes to visit a man who has been breeding a healthier English bulldog for 40 years, but nobody much cares.
That reminds me that you occasionally read, although less often now than a decade ago, of somebody claiming that genetic engineering of humans will, Real Soon Now, change everything. I pretty much asserted that back in the 1990s.
Well, maybe, but leaving aside all the technical questions and consider this: humans have near-complete control over dog breeding today, and yet we are lousier at it than a century ago.