I see what you mean on health issues, especially late developing issues which are highly predictable from genetic tests. Having said that, the rescue I have most knowledge of does full vet checks and will regularly get x-rays and use other diagnostics for anything concerning.
It's mostly on behaviour that I disagree. Genetics sets the boundaries for possibilities, life experiences (including training etc) influences within those set boundaries. Behaviour/personality is really not down to training to the degree that most people think. Personality is malleable to an extent, but only within a limited range of possibilities. There's no such thing as a blank slate. That's why organisations like Guide Dogs get so many rejects after training, even within a fairly small group of breeders.
I'm not saying training isn't important, it's very important, but it can only shift behaviour/personality within a limited range. If I was looking for a specific personality type then I would 100% search rescues for the right adult dog over searching breeders for the potentially right puppy.
Anyway, I feel I'm nit-picking a bit at this point. I meant to write something pro-rescue rather than anti-breeder.