No argument there, but you do adapt, not saying it couldn't be better, but it could be a whole lot worse.
It's really not. They've straight up admitted that this was the way it was designed on the forums once. I'd have to go scrounging to find it though.
There's no reason to program it as they did, but the fact is that they did, and it's just something we have to deal with until/if they fix it. Every fight in the game is choreographed, so it's pretty easy to determine when something is going to come (IE: Twintania does a plummet every 3 auto attacks, does a death sentence every 3 plummets).
There are some very, very minor exceptions to the rule of "enemy cast bar = calculations done". Off the top of my head, KB's meteor in CT has the hit/miss check done about when the meteor physically hits the ground. Not knowing this, I stepped out as soon as the cast bar finished and still got whomped :P (Edit: Also to a lesser extent, if you kill an enemy before their animation finished [or rather, before the damage registers] you can still cancel it that way).
But for the most part, yeah it's not a crippling issue. Mind-meld with the enemy AI better. Not like it's going to change anytime soon. Think inside the box.