Just after you finish the two groups of Taken, you will have a Taken Ultra to deal with: Balvog, Shield of Oryx. Move either to be among the pillars on the side the Dreadnaught or go past Balvog and use the raised platform and its various parts for cover. Keep on the move throughout the fight. Try to get some of the Cursed Thralls that are appearing to explode on him. They do heavy damage and there are usually a few groups of them.