I can tell you why I don't spam AoEs as a samurai: I would actually like to be able to attack. Fuga -> Mangetsu/Oka is a combo that flows pretty well, but it's such a massive drain on my TP for not nearly as effective damage l, because of falloff, as, say, my bard, who can just put up Mage's Balled, throw out some DoTs, and have unlimited Rain of Death. Now, of course I use Kyuten and Tenka Goken when available, but without a TP generating ability, just spamming my AoE combo means I last for about 20 seconds.