Yeah if you bond with a dog, I don't think anyone would rehome them. I have seen cases though where the person didn't bond with a particular dog for whatever reason and when rehomed, the dog does a lot better and the person also does much better with a different dog with whom they do bond. I wouldn't rehome Sammy even if he broke every bone in his body, he's my dog now.
Separately though is the issue of rehoming if the dog is not at all what you're looking for.
When they're young, and you want you a dog to compete with, you've done it before and at 4 months the dog is really starting to show that it will never be a competitive dog, well I don't think there's anything wrong with rehoming. So long as you find a good home for them. You take a dog on, you're responsible for them but that doesn't mean they need to stay with you.