yes, both characters only get 2 extra atb gauges. you can get a third one with weapon equips --- There are but two types of fights. Whenever we go into battle, it must be one of the two: The fight to protect life or the fight to protect pride!
In the first incarnation of the game, you similarly had to equip the character's tier 3 weapon to gain the 6th ATB bar.
Only issue here is that while in FF13 most characters would end up with tier 3 weapons post-game as they were generally much better than their tier 1 and 2 counterparts, the weapons that confer the 6th ATB bar in FF13-2 are very underwhelming and seldom used. --- Burning with anger, the ArchDevil hits the Archangel for 150% damage.