Even having not played it all the way through, and despite liking P5 way more (it’s one of my favorite games in spite of the glaring problems), the series hasn’t really beaten P3 yet in themes and the aforementioned character development.
It doesn’t front-load each character’s core narrative arc, and their Persona transformation is tied to a major pivotal moment for them late in the story (rather than through resolving a B-conflict via a Social Link), so you get a better sense of buildup to that moment.
Plus the overarching antagonist of “societal apathy” totally works because everything in the game is thematically tied to that, right down to how characters summon their Personas. 4 and 5 try to recycle that idea, but it falls flat because neither of them are even remotely about societal apathy.
(also it doesn’t have anywhere near as much ignorant, gross stuff as those later games)