Personally I believe that power comes from personality, personal strength, intelligence, and of course sheer dumb luck. The Fool or "Wild Card" symbizes someone who is open minded, but has a lot to learn. And as the residents of the velvet room say... "limitless potential."
As for the Kanji vs Akihiko thing. kanji is naturally a big guy, I don't remember him ever saying that he performs any specific flavor of training, so he is a "naturally big Guy. But since he is open minded and more "feelsy". He most likely will have stronger PERSONA powers, not stronger fighting skills. As an Akihiko main I realized something important... He rarely uses his persona. Aki actually has little to no use for it sometimes. So Aki has better physical skills, but far less persona skills. Another aspect of his character to acknowledge is that Aki is a very closed off person and unlike Kanji who was unhappy due to be closed off, Aki seems absolutely ok with it.
Lastly is involving tarots. Mael and I discovered that how tarots are assigned are often completely random or "chosen by fate". Every month of the year and Zodiac has a tarot aligned with it. I am pretty sure that the creators of the persona series are fully aware of this.
In case you are curious, Mael's Tarot is the Star and mine is the Hierophant.