Originally Posted by
Ekimmak
Mechanics in general make that a really bad idea.
Even if you decide that you don't need BRD/MCH's ability to recuperate TP/MP, or the melee/mage limit breaks, there's plenty of savage fight mechanics that would become extremely unpleasant purely from the fact that you're expected to have 4 DPS.
*Catastrophe's tentacles, purple debuff, and -100gs are suddenly not getting applied predictably.
*Hallicanarsus will destroy you in her first board game, and likely kill the healers on her thorny board waltz.
*Flare is applied erratically by Exdeath.
There's enough gameplay mechanics in place that even if tanks were equal to DPS, they wouldn't flat out replace them.