I don't really think that you need to know the fight 100%, you just gotta use some common sense.
You can kinda feel a mechanic coming, if there hasn't been one for a while or if there just recently was one.
I can't really think of anything that would happen so quickly that Assassinate would mess you up.

Not saying that things '' should '' be animation locked, altho I actually think that it has a nice feedback to it and it makes sense since you're kinda latching yourself unto the boss/ mob.
It just feels good to use imo.
I just can't think of ever feeling like it was an issue, new fights included.
And I mean you use it in your Trick Attack window right away so if you have to abandon the boss to move away you've kinda already messed up.

But yeah NIN is one of the Jobs the devs tend to give the most attention *cries in MNK*.
So solving stuff later isn't out of the question.