Flavius is all about controlling your enemy. He does well with Herja, and you need to pay attention to the order in which they act. You also need to consider when your enemy's Herja acts and when you enemy's Flavius acts.

I love Flavius. I use him all the time. That being said, he is weak, not to say uselessss, against the heroes who have morale retention, i.e. Pompei, Bloodstorm, Genghis Khan and Scipio Africanus. It is almost impossible to prevent them from using their skill attacks when Herja is with them.