Quote Originally Posted by Silverquick View Post
No they actually won't (be consistent/predictable), because damage is not constant, so the Boss mob getting to that transition phase is not constant, either with your timing nor your CDs. It COULD turn out that way... but it also might not.
Have you ever compared two groups with vastly different DPS on fflogs? While there is some variation, the encounters tend to line up with each other pretty well.

I guess you're not wrong in saying that variation exists, but there isn't that much of it. 95% of the time your best option is to follow your rotation. As I've done more end game fights myself I've found that sticking to your rotation is a very common answer to the question of optimization. If a mechanic forces you to disrupt your usual sequence of actions, you're probably doing something wrong. There are exceptions to this, but they're very much exceptions.