I tried that dark mission on the very first day of the event (and my very first rag, didn't even bother doing it with fire team first, it wasn't burst time either) and I won the first time, but I did lose 2 himes..
I'd say it can be quite hard to win if you don't have any form of defensive options like pluto/joan's damage cuts w/ some Tiamat barriers and maybe some form of heal plus a dispel if you can bring it to survive multiple raging ODs since it hits quite hard with the atk buff on even with 50% atk debuff cap