As @omgFIREBALLS already said: the fight is winnable without any DLC content.
If you wait too long it might even feel too easy.
Single target damage dealers like Rogues, Fighters, Paladins (unless they already have Sacred Immolation), Rangers etc. are not as useful in this battle because there will be so many enemies and targeting single enemies isn't as effective as targeting many. Although they can use spellbinding gear and scrolls of course. A high accuracy Fighter with good INT and MIG, equipped with Rotfinger Gloves for example is nice. Should you have a Rogue with Deathblows and high Lore then make sure a bunch of enemies suffers two afflictions that unlock Deathblows and then use a damaging AoE scroll (non-DoT) or spellbinding (Taluntain's Staff for Fireballs for example) with him: Deathblows will grant +100% dmg to those spells.
AoE is king here, so bringing Wizard (Chillfog, Walls, Combusting Wounds, Kalakoth's Minor Blights + Blast/Citzal's Spirit Lance), Priest (Shining Beacon), Chanter (Dragon Thrashed), Druid (Relentless Storm, Overbearing Wave) and Cipher (see below) are good.
Especially Ciphers can shine here because there's so many weak enemies to farm focus from - and then turning it into AoE CC and damage. Ring Leader or Amplified Wave are excellent tools in this fight (if you already have access to them).
Monks with Torment's Reach and high INT as well as an Overseeing item are also very effective since it's easy to hit a lot of enemies at once. And it's also easy to get wounds...
Barbarians can have good effect with an overbearing or stunning weapon and high INT - and if they already have Blood Thirst it should be a field day for them due to the many weaker enemies which will allow to proc Bloodlust and Blood Thirst often. If you have Heart of Fury already then combine it with a Wizard's Combusting Wounds and a dual weapon setup.