Gwok Jing is notorious as the "dummy" of Jin Yong wuxia while Cheung Mo Gei, though not brilliant, is generally regarded as a fairly intelligent person.
In terms of being wulin savvy/streetwise, however, was Cheung Mo Gei actually "dumber" than Gwok Jing? Although it's true that early in LOCH, Gwok Jing was as naive as they came, by the end of LOCH (and certainly by ROCH), it wasn't easy to deceive or take advantage of him...or expect him to blindly walk into a trap. By comparison, Cheung Mo Gei, from the beginning of his adventures to the end of HSDS, still seemed to be an easy mark for wulin tricks and deceptions. Although it's true that Gwok Jing had Wong Yung to offset his naivety, Cheung Mo Gei also had wulin-savvy people such as Yeung Siu and Chiu Mun, but he never seemed to internalize an independent wulin savvy the way Gwok Jing did.