@musicfreak12 as far as I remember, there were indeed no betrayals in Alesia. However, the Gauls tended to break or betray too fast throughout the conquest of Gaul (hence "the whole conquest of Gaul" and "surrender or betrayal"). In Alesia's example, the Gauls broke too fast, even when they had the upper hand in sheer numbers.
Relative to the old phalanx method which was prevalent at the time, the maniple was more flexible. You're correct about the recruit-regular-veteran stuff, but that's not all. Here's a really good short video that explains it better: https://youtu.be/3iz1_UwD2Fw
That channel should also give you much info on Classical military stuff (mostly Roman), including Alesia and the conquest of Gaul.