I asking why he isn't as strong as Saiga, Senzui, Mikumo, Jenezad. He's a super genius, he learn most things in a couple seconds. The only thing I think might not be able to learn easily is the heart, because Rachel said something like even geniuses can't learn the heart easily (referring to chikage). Sometimes it seems that Akisame has trouble seeing things from other people's perspective too, like when he trying to understand Shigure's father wish for him to kill him.
Even if Akisame can't understand heart easily he understands the body and martial arts techniques really well.