Zodiark and Hydaelyn pre-date the Shards (and most likely the life on the Shards/Source). We aren't even really sure if they are tied to Light and Darkness at all, just that Hydaelyn seems to use Light more and the Ascians use Dark more. And we also know that Hydaelyn wants to preserve life while the Ascians really don't care about it.
It's not that much of a stretch to think the Ascians got their stance on things from the divine entity they claim to worship.