In normal mode, 3 symbols last more than 3 seconds, and it is easy to fill up the gauge to full. It increases when Dante attacks and recieves damage.

Why would Dante be hit for sure when he lands? The arena is a huge open area, I don't think Auron can get close to Dante that easy. It will take Dante about 1 second to recover when he lands (By recover I mean, he can start rolling and everything.) Can Auron get close enough and hit Dante at in such a short period of time?

It won't be a wise thing for Auron to stay close to Dante when he's in the Air shooting lightning, because it will hurt. Dante doesn't have to fly to Auron while he shoots, so there will be a distance between them, and giving Dante enough time to land safely.

In the mid of the battle, Dante can just switch to Ifrit, and dodges most things with Rolling Blaze. Engulfed in flame when he jumps (and invincible when he jumps), and at the same time damages and stuns (Or more like breaking the enemy's move) the enemy.

Dante can also equip his Bangle of Time (which freezes time, at the expense of using the Devil Gauge) and freezes time as Auron is about to use his Overdrive. With a full gauge, Dante can freeze time for about 20 seconds to half a minute.

(It is not classified as an item because Dante actually equips it. You can see it on the screen, even.)