Lightning is more main character than you think.

My team is:

Lightning, Fang, Vanille.

During the storyline you need every character. Especially Hope because he is fast at learning Magic like Protes, Shell and Haste. Of course everyone can use the Enhancer job class, but first their Crystallium Board looks different and so it needs a different amount of Crystal Points to get from one spot to another. And so I've used Hope during the Final Battle. He was a great help, even with low Hit Points.

I was happy when I got the "Battle Member Change" option. Sometimes I just want to use other characters so I am glad you are able to change your party (but not from the beginning).