I use my Necro to 55 the Djinns in Hidden City HM. Any group consisting of 2 roaring ethers is very hard if not impossible, but a group with only one is doable as long as you hit the ether first with Spoil Victor and just cast your enchants when you can. I've never tried for the boss here as he is surrounded by more ethers every time I go in. Great farm for dust as well as a tiny chance of Rubies or Sapphires or Diamonds from essences, and an occasional fiery dragon sword drop. And yes, tons of Vabbian Defenders.
A note - I can NOT farm this area without 15AL armor and Spirit Bond on my bar. The Diamond Djinns and Ruby Djinns aren't the problem per se, it's the burning stacked with the Sapphire's scythe attacks that does it. Once the Sapphires are gone from the group I don't need to use Spirit Bond much if t all. I attack in this order- Ethers, Sapphires, Rubies, then Diamonds,which will seem to take forever but Diamonds and Sapphires will heal/buff themselves and each other so best to get the weaker Sapphires out of the way first.
[Protective Spirit][Healing breeze][Spirit Bond][Necrosis][Spoil Victor][Essence bond][Balthazar's Spirit][Mending]
I don't run a 55 monk so sorry I can't provide a better build/advice for you