For the majority of fights there's literally no reason to learn the entire script by heart.
Not even for Titan HM/EX.

It's enough to know that bad move Y comes after X, and just react to other steps as they happen.

As healer I always keep an eye out on the entire battle.
When I go dps I do tend to tunnelvision a lot though which I'm guessing is the biggest problem for other dps as well. Learn to "zoom out" and you don't have to memorize the script as much.