Just recently i used and All-Merc army in my Pergamon game. It had its reasons though. basically, it was to represent an alliance formed by my FMs and Ephesus, which was tired of Seleukid rule in Lydia...so recruited a "merc" army in Lydia as the Ephesean army...went and took Sardis...made it allied. So i plan on doing all or mostly merc armies to represent city-states in the areas that arent shown in game, such as Miletus, Ephesus, etc