There are acknowledged problems with pure breeds of all kinds, but not all pure breeds suffer from such extreme problems. It's possible to find a breeder with a strong bloodline free of many defects but it is not going to be cheap.
I've owned mutts my whole life, mostly medium-large dogs that you'd expect would suffer from hip dysplasia and so on, but they've all lived to ripe old ages and they've all been smart as a tack. Hybrid vigor is awesome.
The Shepherd isn't even a year old yet and she looks like she has trouble standing up when she's been laying down a while. Maybe her legs just fell asleep, I don't know.
She was free. Some family has them to keep with the livestock, and they bred them--I took the runt.
The mutt looks mostly boxer to me, the pound said boxer/shepherd mix. She's beautiful, very smart, and loyal, and just incredibly quick outdoors--best dog I've ever met.
Anyway, just my one data point.
A "pure" gene pool can only get smaller, never larger.