Gwok Jing is notoriously depicted as a "dumb" person, and in terms of being quick-witted, articulate, or able to think complex thoughts, that is not an inaccurate assessment of his character. Gwok Jing, however, was first and foremost a martial artist and a fighter, and in this aspect of his life, he was...surprisingly, not particularly "dumb" at all. Looking at the long span of his career in wulin, I can't think of a single occasion wherein Gwok Jing ever lost a fight because he made a stupid decision in combat. Whenever he lost fights in LOCH or ROCH, it was only because he was overpowered/overwhelmed by more powerful or more numerous (or both) enemies, not because he had stupidly made a mistake in his fighting judgment.
Compare that to supposedly "smarter" fighters such as the Golden Wheel Monk or Cheung Mo Gei...