It occurrs to me, Elidibius didn't quite say that there *had* to be a balance between Light and Darkness. What he said was 'Things are tipping too far towards Light, any further and *our goal will fall out of our reach*' Paraphrased, but that's more or less it. The Ascian's 'goal', of course, being the revival of Zodiark.

I think what he was saying is the Light, thanks to the WoL, was on the verge of a descisive victory that would, if not permanently prevent, *severly set back* their goal of reviving Zodiark.

The Ascians are trying to tip things towards Darkness. At no point did Elidibius say they wanted balance, merely that 'balance' in terms of an eternal tug-of-war between Light and Dark existed. Just my take on it.