I also found the episode Lisa the Simpson to be funny but a distasteful episode with questionable message.
Bart never seemed to be a dumb person but rather a unmotivated person secondary to bad parenting and lack of role model from his father Homer. There have been times when he seem to have leadership ability, social skillsand showed some cleverness. In fact I think he has more likelihood to be the president of the United States than Lisa Simpson based on his personal characteristic.
Episodes that spread message that people are inherently dumb and are essentially a lost cause I find to be distasteful especially when it always seems to be that Bart seems to have potential just with poor guidance from Homer