Well IMO they will be much like Vikings and Woodsmen in MTW, much like peasants but superior and more effective in the early ages before the seperate factions get their legions developed. Once legions become truly developed gladiators will become out of date save as a policing force, much like Urban Militia and normal peasants. Simply overreacting about a unit before you even know how it performs is quite ignorant. It was probably released the first because it was so easy to define it and its purpose, whereas to develop the Velites, Hastati, and Triarii will take more time to truly define them.