The reason why people are saying the fights are straight forward is...because in the literal sense it is. Everything is scripted and occurs on a rotation, pattern or boss hp (which is now displayed by a %). The closest dynamic mechanic I've seen is the spawn location of certain adds (such as bulbs and renauds), but dealing with them is all the same.

The real challenge is getting 7 other people who are willing to commit to a group and learn the fights. Every group does the fight differently, and while things are simple on paper, you still need to have first hand experience to be able to work on it. When you have to replace people in a static or PuG, you're at the mercy of them being on track with what you know, or essentailly have your progress reset when someone within that static bails on you.

My static has been stuck on T7 for the last week because every raid night someone bails out on us at the last minute, causing us to start an hour late and have to PUG someone (who would then also bail on us after 2-3 wipes, despite it being a progressive/learning static)