OK, not to continue this into 'ab absurdo' territory, but it was luck of the draw, probably. If by "interbreeding", you mean cross breeding with other breeds, I agree. Breed crosses may produce nice dogs, but they( e.g. "Labradoodles"), are not labs. Unfortunately, the number of responsible breeders who carefully monitor their stock for weaknesses are so far outnumbered by the puppy mills and typical backyard breeders who advertise in the local paper that it makes finding a quality specimen a real challenge. I think the European (i.e. "English") Lab stock is vastly superior to the American in regard to health and robustness.
As for what need I would have with a good sport dog, I do find "soft mouth" an important trait, as well as not being "gun shy". Those dogs who are gun shy tend to be highly destructive and anxious in thunderstorms, (boy do I have first hand experience with that!). Of course, the better they are as retrievers means the more tireless and incessant they will likely be with that slimy tennis ball.
I have had several sporting breeds, including Irish Setters and Labs, and no doubt they are wonderful dogs. A little boring, but solid.