A friend of mine breeds and shows them. I have NEVER seen a breed that is so consistently dumb as a box of rocks (American Cocker Spaniels can be as dumb as an Afghan, but they vary more in intelligence. I do know some smart ones). Afghans are gorgeous, but like beauty queens they've been bred for that to the exclusion of everything else.
My Labs are the opposite - they're bred to pick up ducks, and as far as the field Labs are concerned nobody cares what they look like, so long as they shed water and can run like blazes.
You are confusing difficult to train with dumb. They are mountain dogs from Afghanistan (hence the coat) and an ancient hunting breed related to the other sighthounds (greyhounds, borzois). They hunt at long range and independently, which is why they are independent. They are good at hunting independently because they are extremely intelligent. They are also stubborn and larcenous.
Because they are difficult to train, which is related to their independence and disinterest in whether or not their owner is pleased with how they do tricks, they are not a breed for everyone. Despite all they are extremely loyal and excellent guard dogs.
Of all the breeds I've had, Labs are not among them. I've had contact/second hand knowledge with them via friends and they are often quite a handful as pups but mature into to great dogs.