How does that even work, considering Bell still needed to fight the minotaur well above his level? I'd say this anime adaptation would make more sense. Bell would actually still be in a shape to put up something of a fight.
Sword Oratoria suggested Ais is partially a spirit, not fully human. I'd say that lack of personality is her personality. According to Ouranos, spirits were helpers the gods sent down to Earth to assist heroes in the fight against the monsters. A complete human like personality is not required.
I like Ais. I don't mind if she keeps bashing Bell's skull. He needs that. But then again, the series has a whole lot of great girls.