Not stupid, just designed for different purposes. In the hands of people who know hounds, they can compete in Obedience and Agility as well as sports they were bred for. I know of one Afghan that was doing advanced Obedience and a Rhodesian Ridgeback that was up and coming in Agility. Terriers another group of dogs primarily designed for hunting. Smaller terriers like the Scottish Terrier and the popular Jack Russell were bred to hunt smaller game while larger terriers like Airedales and Kerry Blues were bred for larger game and also to be all around farm dogs.
Terriers tend to be tenacious and in the wrong hands can be trouble.
Terriers are tough dogs and tend to be quite self-willed. Think seriously, terriers go into a hole by themselves and have to tackle critters sometimes quite larger than they are without a human helping. These dogs have to be tough and able to think for themselves. Terriers may have their own agenda with life and may require a firmer but still fair and fun hand with training. Some breeds worked closely with humans like Dobermans while others worked alone like Great Pyrenees .