This one get into the crux of the matter. I keep complaining to my friends that this game doesn’t even try to introduce you to game mechanics when it matters. Final Fantasy XIV on the other hand takes you in step by step, and every boss fight has gimmicks that make them different from each other (and even multiple difficulty levels in the case of earlier dungeons).
This game basically reinforces the idea that, so long as you have class XYZ combination, you can just stroll around everything and then suddenly spikes the difficulty with little in the way of reason. All this stuff should have been the obvious design elements from the start.