Aside from when I was very young, and my family had pure bred bull mastiffs and earlier dash-hounds, all my own later dogs have been mixed breed, pound retrieved dogs. These earlier kennel raised pure bred dogs, as I remember, were easy to deal with. Just off the shelf, here is your dog and it will behave. All of these pound dogs I later got, had problems. I would take on the problem dogs as we lived in the country and I thought I knew enough about training dogs that they would come around. Our current dog, is the best of dogs, yet he has his issues. He is getting old and still has his issues. He can't be around other dogs at all. He will immediately attack any dog smaller than him. I believe this now to be the most difficult area of having a pound dog. Some things, you can not train them out of, cause they are sort of fixed.. Especially about them being social to other dogs.
So, for the jury to decide, do I get my last dog, after this one passes, from a breeder/trainer and not the pound? Or does it make any difference?
The biggest advantage a "breeder" has is the fact that because it's a dedicated breed that perhaps someone will spend money on, the dog is generally in the home as a puppy to be raised and "molded" by the house it's living in.
I also think your generalization that "here is your dog off the shelf and it will behave" (from a breeder) is WAY off the mark and not true. The behavior has more to do with the training at an early age vs the breed itself.
Will a child in foster care who is adopted out at age 8 vs age 16 have more or less "issues" than the older child adopted out of foster care?
Ironically enough, even babies who are adopted out after being removed from their birth mother can have more issues than you realize due to separation from their mother (not including perhaps behavioral issues passed down, that's way more than I would want to get into).
That said, even siblings born and raised in the same family who have been shown the exact care, love and discipline up until age 18 can turn out to be completely two different people, one with some great traits, the other with some horrible traits.
The above 3 paragraphs can be said the same for dogs IMO.
The issue with dogs is owning one costs money. A lot of people who get dogs shouldn't own dogs in the first place IMO (why do most end up in the "pound". The other issues with dogs is training at a young. You also hit the nail on socialization.
If you look for a "rescue dog", I'd take a look at groups who foster animals. When we fostered dogs and cats in our home, some animals would be with us up to a year before we found the animal a good home. The advantage of dogs in foster care is that as someone interested in adopting the animal, you should find out all about the animals traits, both good and bad. Perhaps even a dedicated breed rescue group. Keep in mind, dealing with people sometimes can be harder than dealing with the animal.
End of the day, a shelter is the WORST environment for a dog to be in for a host of reasons and isn't conducive to good behavior.
All 6 of our dogs currently with us have been "rescues". The biggest pain in the butt dog came from my neighbor (long story), who was an idiot himself (who thank God finally moved) and I don't blame the dogs behavior on the dog, but the owner. That said, two 11 year old sisters we took in from my MIL after my FIL passed away in January of this year. They were raised in our home as puppies and adopted out to my in laws at a "puppy age". 11 years later, they can still fight with each other like grumpy old sisters LMAO
My wife and sister were raised in the same family, shown the same morals and financial training along with a host of life skills. Funny enough, my wife and her sister are nothing alike, and thankfully I married my wife and not her sister LOL I just scratch my head on how they were raised in the same house.
Good luck in your search. The safe bet is to spend good money from a great breeder, but then the rest is up to you to train the dog that will increase the odds you shouldn't have "issues". Thing is, like humans, even then I honestly believe it can be a hit or miss, because like humans, no two dogs are alike.