There have certainly been a few breeds destroyed by the show ring. Bulldogs that can't give birth other than by c-section, german sheperds with that ridiculous sloping back(working lines have much better structures) etc etc.
As for mutts being tough as nails, it really depends on what has gone into the breeding along the way and probably how many different crosses are in the dog. A lot of these stupidpoo crosses have all sorts of health issues because the people breeding them know bugger all about breeding and don't health test their breeding stock so they unknowingly include dogs that should never be bred from which introduces all sorts of weaknesses and diseases.
I really do wish it was mainstream knowledge that pretty much all of these stupidpoo crosses come out of puppy farms. So everyone who buys a labradoodle or a cavoodle or any other stupidoodle is actually supporting puppy farming and the horrendous practices that go on in those places. Baird banned greyhound racing while ignoring the elephant in the room when it comes to animal cruelty.
