Easy kill with THF/NIN and WHM/BLM. Capped Shellra V and MDT gear when he flies. Try to stun Dread Spikes or steal the effect. Easy to just melee through them till they wear off. By far not a hard fight at all.
I feel ya man, you just have to get used to little kids knowing nothing about anything.
Furthermore, Empousa is a pretty tough NM. MNNK/WAR tank has been the best i've seen so far. Even pulling empousa to the Martello for whm/rdm to fill back up on mp has not been enough many times. 2 WHM highly recomended