Well it kinda makes sense when they made espers useless. I mean think about it, many people used summons as a cheaper way to beat bosses easily in the past FF games, so they wanted to make FF12 look more different, they also made it look a bit more difficult by balancing the use/power of epsers and normal attacking/magic, etc, i guess...

Though if they made espers more useful, it would bring me back to memories of playing the past FF games