You want to know a reason why people find FSoF and such so difficult?
Because each of these raids starts over with a completely new song and dance routine, and each one must be memorized on its own from start to finish. There is very little actual "skill" involved in most of this game's hardest content; it's more about memorizing a script and, sometimes, recognizing when it's your turn to do a certain dance move. There is extremely little reading and reacting that goes on in this game. If that wasn't the case, then you'd see less of a gap between people who played 30 hours per week and have statics vs. folks who can only play 10 hours/week and not at consistent times.