User blog comment:B214/Talk About What You Want! 2/@comment-24173056-20140703131554/@comment-1359322-20140703133249

You can't call that cowardly, like Jop and the anon said, strategy =/= to cowardly. If that were to equate to cowardly, then almost everyone in DxD would be considered as coward. Sona used Saji to suck out Issei's blood in Volume 5, even went as far as to create a hologram while hiding in behind. Does it make Sona a coward? No, Sona was aware of her goals and purpose.

In the end, it's just how the battle went, Cao Cao took advantage of the ORC + Vali Team's weakness to win and complete his goals and purpose, it's not cowardly at all, It's just a simply, use the opponent's weakness to win. Even Issei does that, he did it to defeat Riser, he also did it to defeat Cao Cao in Volume 12.