*facepalm* No... Get Pluto first and then you can MT Berith later.
Pluto will keep your team alive, give you buffs and she will burst like a truck.
Berith is awesome but she will shine more later with the new LRag. However that's months away.
You want to improve dark and you dont have Pluto and Berith, then always you go like that:
Pluto > Berith.