User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-26527700-20150720200408/@comment-26527700-20150721003326

I get what you're saying to a degree, but even with the stress of seeing others fight for her, Asia is the kind of girl who is more concerned with protecting those she cares about than she is about defeating those that are harming them. Unlike Ise, who beats down anyone who messes with his comrades, Asia is more likely to try to use her own body as a shield to protect injured allies. Ise would move the ally to safety and then beat the shit out of whoever hurt them. Her ability is the perfect reflection of this. She can now protect herself without other helping and simultaneously defend and heal allies.

Think of it this way. If Asia had this ability during the RG against Sairaorg, Rias and Ise wouldn't have been so worried about bringing her along for the final battle.