You want to see hard with tons of one shots :
Akilyios (Rift):
http://www.youtube.com/watch?v=662OoYUvgwE
There is nothing in FFXIV that even comes close to the difficulty of that fight. But yet we pugged it hundreds of times.
I am starting to see a trend though, and some comments here do bring an important point to mind... A lot of the mechanics can cause fail conditions for another person even if both people execute their part correctly. I.E. Titan extreme if people don't stack, you can end up with weights in bad spots where 2 people might dodge their own weight but end up running into another persons. But even that is debatable as it can be prevented by just stacking or just... not running into the other persons...