The Evade special rule gives formed units the ability to respond to an opponent's charge by moving directly away from the charging unit and continuing to face it, just like skirmishers do. The main difference is that formed troops may only evade charges originating in their frontal zone. However, they also have the ability to charge or counter charge heavier opponents, which skirmishers cannot do. So the question is, do you believe that the historical role of Late Imperial Roman Illyricani and armored horse archers was to serve exclusively as skirmishers, or to be more flexible with the ability to evade, shoot, and/or engage in combat, depending on the situation?
"Experience is the teacher of all things."
~ Gaius Julius Caesar