My personal darksteel theory is that they actually ARE Derplander and company, but something went wrong when Louisoix sent them into the rift.

I think Zodiark may have "claimed" them as his own and they've effectivly been brain washed into the Warriors of Darkness. That "Short" five year trip into the void actually showed them how a world that Zodiark wanted them to believe was going to be Hydaelyn fault and then promptly erased their memories until Elidibus (Whom I still believe is Zodiark incarnate) called upon them to "Restore Equilibrium" and thus the Warriors of Darkness went looking for us and, as they did in the past, destroyed any primal foolish enough to cross them.

But to them, The Scions never existed, the Path of the Twelve is Destroyed, Louisoix is Dead, the Archons are with a "False Hero" who's claiming to be the Warrior of Light now, and they are planing to "set things right" on behalf of the Ascians.

Even in FF3 where they originate the Warriors of Darkness were never evil simply the defence against the light becoming to powerful. Which could be the case if Zodiark=Darkness and Hydaelyn=Light. The clash may even result in both deities being awoken or sealed thus forcing an "Equilibrium" between the two.