I know the archetype of shonen characters is that they aren't too bright but even Goku or Naruto could get serious when necessary and they showed some knowledge, Luffy through all One Piece hasn't changed much apart from getting stronger. He makes very stupid and dumb decisions, constantly repeats "I'm gonna be the pirate king" and the only things he does in life are fighting and eating. When he has to do "intellectual" stuff side characters have to help him because his only talent is being very strong and having powers. Also how he doesn't know how to speak in normal tone (always shouting) and doesn't understand social interaction like he's about to die and can keep laughing or a hot foid tells him if he wants to marry her and he says no make me suspect even more he's mentally challenged.
