I think it says it all that the "True Final Boss" of P3 doesn't feel like a "True" Final Boss, it just feels like "The" Final Boss.
Technically The Hanged Man could be the final boss of this game and the very idea is hilarious. P4 does it TWICE, and you can technically end the game after any of it's 3 final bosses. P5 is the worst at this, I don't think that's controversial. I'm actually, and I think this is the minority, am a big fan of Shido as a character and would have loved to have just built the game up more with him as the actual end. I don't find much value in the post Shido stuff. Maybe if I care about Morgana even, like, a little bit.