I know literally dozens of people with GPAs >3.75 who are not remarkably bright. I have yet to meet someone with an MCAT 34+ whom I did not think was very smart.
Of course a high MCAT signifies that you're obviously an intelligent person who would think otherwise. A high GPA doesn't mean you're a genius but you are a hard worker who toiled for years to earn your GPA. Grade inflation/deflation, easy prof, easy school whatever excuse people give more often than not those people have worked for that GPA. I haven't met a person with above avg GPA who wasn't a fastidious worker. Just because you are not remarkably bright doesn't mean you are not an intelligent person. I really don't know what your comment has to do with the price of bread anyways. Who was saying that those with high MCATs are not as bright as those with high GPAs?