Bismark EX doesn't have much randomness to it... It is extremely straightforward with a dps check - if you can remember your dps rotations. Is this what you call challenging/difficult?

And really... most of the people complaining that coil mechanics are scripted and reading a guide/watching a video is what you need to clear it, never actually done it.
I'll agree once you get the mechanics down it is not that hard to get 8 people to do team jump rope. But it takes a lot more practice than what Bismark EX is offering - kill adds - fire dragonkiller - jump on the sky whale - repeat (which itself is very scripted). And guess what... once you learn it - it's not that hard either? This is challenge?

Let's see what's your idea of difficult/challenging that is not a complete faceroll.