I got a 5yo GS from a shelter. He seemed nice enough. He wanted us to love on him, and wanted training. This was a Friday. He tried to kill 2 of my cats and attacked one of my horses in his stall. This guy was young enough that he still pee'd squatting. Monday I took him back to the shelter, in a crate. Somebody had ruined this young dog, and he had no place on my property.
I got my 2 dogs as 8 week old puppies. "Rose," is an (almost) 5yo Husky/GSxBorder Collie mix, and I got her from the owner of the bitch. "Pygma" was 1/8 in a free litter dumped at the horse auction. It was January, bitter cold, and nobody had taken even one puppy. I couldn't stand that so I picked her, and, 4 1/2 years later I still own her. She is (the best we can figure) Lab/GSxPitbull. She is a great watchdog but she bristles, barks, backpedals and lets Rose do the dirty work. She is wary of ALL strangers, but if my friend will sit down and visit for about an hour, she will flip their arm up to be petted, and then she makes fast/forever friends.
Last summer my cat brought home a stray that someone had dumped, 1 1/2yo miniature schnauzer, hungry, dirty, needing worming/clipping/
Spaying and STARVED for love. We had her only 3 days and she was jumping in our laps, let her carry her around upside down, and sleeping in a crate trying SO hard to be good enough so we wouldn't dump her, too. I don't need a little dog, but my friend, who also had the same kind of dog, adopted her and her dogs both get along fine, now.
It's in the breeding and in the training. IMO, you cannot make a blanket statement about any breed of dog, or breed of horse, for that matter.