Another thing to recall is Elidibus' status as a primal avatar of Zodiark. The exact mechanics of this are a bit murky, but the point is that he is effectively himself a Primal of Salvation, be it as a part of Zodiark or as something bound to Zodiark.
It therefore follows that the wish and intent with which Zodiark was summoned is itself a part of Elidibus' inherent nature, right up to his death. That nature being the charting of restoration for this Star which brings it salvation and restores order.
It therefore follows that Elidibus is inherently meticulous, his plans are comprehensive, and he doesn't tolerate chaos beyond where it is useful to his/Zodiark's objectives. In the big picture, restoring balance matters once the likes of Lahabrea have inflicted some necessary imbalance in service to the cause.

As I see it, in order to beat Elidibus, we had to exhaust him of his options. By the time we fight Elidibus, he is genuinely out of other options to deal with us. The other originals are gone, most of the unoriginal ascians are off the board or missing, and those who aren't seem to not be particularly reliable (Fandaniel).
He had no other options but to beat us then and there if he had any way of salvaging The Plan.

And he lost.