Oh yeah, I didn't even connect the Tarot stuff, that's almost directly relateable to the Persona 3 shadow bosses. I love the idea of your ego being tied to your prowess; as much as I like Fist of North Star-esque fights, it's a great alternative to that.
TBH, I need to read parts 5 and 6 still. The bad translation of 5 stopped me so I jumped into 7 since I knew it was standalone. Now I'm just starting 6, good so far.
The whole ego being tied to your prowess thing is kind of why I have mixed feelings on switchable Personas. From a gameplay perspective, it's probably more fun to be able to customize your Persona layout for your whole party, but I like the extra symbolism and impact that's added when party members are stuck with a single Persona that represents their self somehow. I'm also not a big fan of the whole "the protagonist is super special guys" thing though, but you kinda have to do that if you have unswitchable Personas for party members... Might be cool if they adapted the Compatibility mechanic from P2 and made it so that each party member could only use Personas that they had a certain affinity for. Might work as a middleground, and it'd help distinguish characters.
You've read Parts 1-4, right? Out of all of the parts, 6 probably stands the worst on its own. Part 5 is basically a side story though, I'm waiting on the retranslation project.