Ninja AOE isn't terrible. you can rip things 2 shreds very quickly with death blossom double katon with kassastsu and the hellfrog medium.
Doton I tend not to use because either A. the tank is moving the mobs around far to much. or B. things are dead before doton hits full damage. though if you wanted to you could tcj fuma katon doton and then kassatsu another katon
the other advantage is none of a ninjas aoes scale down on larger pulls unlike samurias.
