That's okay, I obsess over the minutiae of this game's mechanics, plus playing the Japanese version has been like skipping to the end of a book, with all options revealed.
Aokiji is 2x Striker Type HP and Attack. When you use someone like Vista, Asura Zoro or Garp, you can get a lot of HP, but there's only so many high HP units in a particular color.
However, Striker units have some of the highest HP in the game, even in non-gacha. Kraken, Kaku, Smoker, all over 2000 HP at MAX. Go into gacha land, and the numbers get even bigger. Kid goes over 3000, and Moria almost hits 4000. Get your units up into the 90s, and you'll end up with around 60,000 HP. Someday, if we're all super-lucky, we can even
break 80,000.
Furthermore, you can triple buff the entire team with something like
this, although it'll require a lot of Special leveling, and Aokiji is a bitch to farm.
I was wrong about Krieg, though... he used to evolve into a Striker, but apparently that's been changed. I'm guessing the devs didn't like the idea of type changes over evolutions, or maybe it was just a database mistake.
So, TL;DR, you already have a lot of high HP Striker units, which means a powerful Aokiji team right out of the gate.