I had a great shelter dog, and know many who had similar experiences.
People who can’t handle a shelter dog won’t be able to handle a purebred, either.
Yes, and for each good, there is a disaster. Never mind the racket for the last several decades of “adoption”/“rescue” (I actually rescued a kitten from a very weird abusive situation, but that did not involve any middlemen).
Truth is you just don’t know the parents, the upbringing, if any, the environment. Or how many.
It’s not a matter of bravado. “If I can handle it then I’m good and better.” The point should be to get a good animal and minimize problems for family and neighbors. Joy, not challenge.
Knowing the dam at least and the breeder’s environment gives one a huge advantage that is good, not a mark against the owner. Wise picks of character from baby animals. One can mold the animal more easily the way one thinks it should be, than risking an animal with baggage.
I have a cat right now who is my personal first true baggage background, but he is younger and seems to have been brought up very well. Again, no middlemen...just my nephew picked him off the streets and he had too many cats to start.
Bottom line...I handled several purebred German Shepherds from breeders as puppies. No problem.