i dont know about the 20 mob limmit on aoe thing,, ive seen people in tanor canyhon round up about 65 mobs at once and killl them all in one aoe spell atack, i think its the adena farmers but nonetheless ive seen it done
If you have mobs you can kill with one aoe attack, and if you have several nukers so that chances are good that you will more or less "cover" all mobs with several aoe nukes at the same time, it might work. But if you have matk resistant mobs among them, and if you need several nukes anyway to kill them (like the AB mobs), it will get VERY dangerous indeed, especially since the tank will not be able to hate all the mobs back onto him (hate is limited to 20 mobs, too).
The only reliable way to AOE nuke is via summons (unicorn merrow). They are not limited.
Here, straight from the C4 patch notes on the official website:
Changes to Area Attack Skills
1) Physical/magical offensive area skills used by players are now applied to limited number of targets. However, during PvP, all players within the area will be affected. The skill effect is limited to 20 targets and it is unaffected by enchantment. The area skills of monsters/summons are unaffected.
* Wild Sweep, Sonic Buster, Force Buster, Frost Wall, Wrath, Seal of Chaos, Seal of Slow, Blaze Quake, Seal of Binding, Seal of Poison, Hate Aura, Whirlwind, Thunder Storm, Poison Blade Dance, Sanctuary, Sword Symphony, Holy Aura, Howl, Repose, Requiem, Seal of Winter, Seal of Flame, Blazing Circle, Seal of Gloom, Seal of Mirage, Seal of Silence, Seal of Scourge, Seal of Suspension, Word of Fear, Serenade of Eva, Mass Slow, Earthquake, Dance of Medusa, Mass Warrior Bane, Mass Mage Bane, Mass Block Shield, Mass Block, Wind Walk, Seal of Despair, Vengeance, Poison Cloud, Flame Strike, Sonic Storm, Burst Shot, Force Storm, Corpse Plague, Sleeping Cloud, Corpse Burst, Tempest, Provoke, Spoil Festival, Aqua Splash, Eruption, Harmony of Noblesse, Symphony of Noblesse, Shock Blast