Keep in mind that the guide tends to favor a balanced setup more for newcomers; if it's not to your style there's nothing saying you can't change it up. I played most of the game with Fang, Vanille and Hope but when I play again I am definitely adding Sazh in more often for Haste early on. It really makes a huge difference, enough that it'd be worth your while to switch him in for someone when he gets Haste so you can see for yourself. The ATB gauge will fill as fast, if not faster than you can input commands.

Also, every new segment of the ATB gauge you gain will make the entire thing fill a little bit faster. It's noticeable when you have characters with different numbers of ATB segments in your party.

~DragonHeart~