Red and yellow originally had a good, "Mean guy, Dumb guy / boke tsukkome" dynamic that is seen in various comic relief duos in many types of media. Unfortunately, it doesn't work anymore because in left wing influenced media, having a character be mean without either the character being openly evil, or a minority dressing down a white man, is a big no no. So they made red less mean, yellow less dumb, and added a bunch of side characters, and none of them have much in the way of personality.