Well, this fight is the first time you really feel the classes weaknesses.
Theres no killer app direct damage(they use spell formulas), nor buffs that provide direct damage, which means its weakest point, the DR and resists, is significant.
Being immune to fire, plus resistant to most elements means that damaging spells don't work that well, with SR icing the cake(most of the spells that bypass SR go up against DR AND resists).
Battlefield control can work, but with teleportation and again, a lack of butt pounding ability means each control spell would be trading standard actions, with the thing getting a new position or escaping each time.
And since these classes are almost entirely BFC + Direct Damage, well it shows when both become ineffectual.