Well, Bixler, my first dog, got from the newspaper, genetically not the best, Me, 18yo, knows nothing about dogs, training, etc, quickly turned into a bad situation, just as quickly turned around when I realized I was causing a lot of his issues, and I realized that you have to train your dog (and the addiction began!) he still has his issues but with training he's come a long way, and Ive learned a lot about handling a dog like him and how most of the time I triggered his episodes.
Also, In just the last few months I've seen 2 dogs come out to SchH training, having both been worked with 2 different helpers at 2 different clubs, both owners were being told their dogs were basically crap. These dogs might not be national level dogs, but they have both come so far in a very short time.
Dog A, first time on the field, extremely defensive barking, and would hardly bite, the sleeve just kinda fell out of her mouth. The dog is 2 or 3 yo and had been put under a lot of pressure in previous training. This dog is actually turning out to be a nice dog. Its hard for me to believe its the same dog I saw on that first day.
Dog B, apparently people at previous club would run away when the woman brought out her dog, why, I have no idea. The dog is soft if anything. Started her out on burlap rag, built confidence, and now, again, would never guess it's the same dog.
Same with obedience, Ive watched both these dogs, and others come along in obedience, leaps and bounds!
Even with my Hexe, who I thought had nice obedience, a couple months with an excellent teacher and her nice obedience is even nicer!
Ive really come to appreciate having a good teacher and helper
As far as being bred to overcome deficiencies.. I think if you have a really well bred dog, they SHOULD be able to overcome these deficiencies (in less someone is just really stupid and maybe shouldn't have a dog period) I think its more that the dogs who aren't as genetically superior are the ones who are more susceptible to have issues due to poor handling. But that's just my opinion with limited experience.