IOW, I once had an Afghan Hound that was dumber than an inbred snail and I was barely able to teach him basic commands. I rarely observed evidence of much original thought or obvious associations in him. Now with my GS/Border Collie mix, she was not only easily trained, she early on demonstrated she could learn cause and effect connections independently of my training. I'm talking small stuff here like understanding that when I go to a certain room in the house and drag out luggage that I'm leaving for some time, to which she becomes quite agitated. And she has been known to stow away, or at least make an attempt, in my car. The Afghan was simply never was able to put 2 and 2 together. This was tragically revealed when he failed to learn that cars are much bigger and likely to cause great harm if not avoided.
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 correct. Some breeds are smarter than others, generally speaking, and within any breed some dogs will be smarter than others. My Aussie Shepherd/Blue Heeler is very intelligent compared to other breeds as was my Blue Heeler/German Shepherd companion.
I have owned many dogs, and they were/are distinct personalities, if you will.