It's irrelevant in this game because fights are scripted. The mechanics mostly happen in the same order and once you've seen the fight, you know exactly when the enrage cast is going to happen and it becomes muscle memory. It always comes after the script of mechanics that happen near the end.

It's also irrelevant because we know roughly how long it takes until enrage in most battles. 9-14 minutes, except obviously ultimates, because they are not simple 10 minute fights with a single boss. But even then once you've seen enrage you know exactly when it's coming.

If mechanics were completely random, it would be hard to train your brain to expect enrage after a certain pattern of mechanics and the feature would be more important, but they just aren't that random here.