Stamina works much like the cool down timers. just on a slider, only real reason I can see it in place is to balance the whole battle system and put it on a gauge to be controlled by the player (the player feels more in control of their actions) whether it is needed or not is a good question.

I personally would like to see it removed or reworked to a more faster on the ball reaction based style, much like how DA2 dealt with their battle system, or even FF11. Could even go back to the Stances they told us about and work auto-attack into the mix. allowing us to side step stamina.

For a more innovated battle system and instead of watching the stamina bar. we watch the monster, plan the next move. work ones timing to switch stances to get that little bit of extra damage in without getting destroyed in the process. magic users can focus on their distances and watching for Aggro or reinforcements that may hinder the fight.