There is a huge difference between mechanics and scripts.
It's one thing to go into a battle knowing, "okay, there are 7 different skills that this boss can use that I have to watch out for".
It's an entirely different thing to go into a battle knowing, "allright, the boss is always going to use the same 7 moves in the same order... once it hits 70% it's going to add a mechanic, once it hits 30%, another mechanic will be added. All I have to do is move here when he uses this mechanic, move there when that mechanic is used, attack this when that mechanic happens... every time it's the same thing."
That's just not fun when it's the EXACT same thing EVERY single time. Especailly when a few of those scripted actions can one-shot kill people.
You're not testing a players skill at that point, you're just testing their ability to memorize patterns.
In the end, it ends up creating a ton of resentment within the playerbase because you have people who have run the content 50 times yelling at new players saying, "it's the same eff'ing pattern every time, what is so hard about that!"
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People keep mentinoing the word skill. There is almost no skill involved in this game when you take into account that most "top" players just watch Youtube guides en route to clearing content. It's all about memorizing patterns and execuiting the same rotation over and over again while popping the occasional cool-down. What is the skill in that?
Skill is mastering material and being able to apply it in practical situations. When something unexpected happens, you are able to overcome it because you have a mastery of the contect.
Memorizing patterns is the opposite of skill... it's just memorization.
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To everyone who doesn't watch videos and doesn't get help from people who have watched videos. I tip my hat to you, you have true skill. You are in a very small minority of the playerbase though.
I don't watch videos, but, inveriably any time I go into new content there is some "skilled" player who says, "hey... here is the pattern, just move here and do this and we will win"... or, they tell me, "watch the video and we can clear this".
Again, that's not skill. It's memorization and it's what is wrong with this game.
SE needs to stop catering to memorization when it comes to their "hard" content. Throw some curveballs in there and test true skill. Then again, that would be much harder to design than something that just runs on a loop over and over again.