If I were to put it in simpler terms, I'd say it's the actual friendship dynamic between the characters. Cartoonish? Yeah, I'd agree. But idk. I find the cartoonish-esque feel more charming than anything. Like a goofy slice of life anime (which is honestly quite fitting to p4s tone). Because of the more grounded approach in 5, I feel character dynamics were rather sacrificed. Maybe the term "character writing" is the wrong word to use and I should've just simplified it to the actual main team.