I don't think people even know what "style over substance" means anymore. They just say it because it's smug. If anything, there's too much substance for one playthrough in even the original P5. I've played every game from ATLUS and P5 has easily the most substance out of all of them, despite not being my favorite. There's so many areas, minigames, activities, and countless missable full events for each non-story progression social link that a player trying to game the social links optimally would never see because they aren't rank-up events, and I hear Royal only adds more substance on top of it. And with the stealth dynamic added to dungeons, you can turn it into a stealth game with retreating from palaces with high security by slowly sneaking your way out on low SP.

Style over substance would honestly apply more to Metal Gear Rising. That game has a lot of design issues but is heavily carried by its presentation, animations, music, boss fights, and zandatsu system.

Persona 5 - bad design decisions fueled by excessive artistic overload 

even the UI in is game is unnessesary "stylish and cool" with all these "creative" fonts over the menus which even make things unreadable and incoherent - that's what i mean by style over substance 

but anyway i'm happy you love it, maybe i will change my mind someday