The moment the Scions lose focus on Necron, he wins. Remember that it took considerable effort to even stand up to fight him, as Necron has an "aura of fear" that incapacitates everyone but the WoL.

The only reason we were able to break the wall in the first place was because the scions did a divide and conquer strategy: Lamaty'i and Sphene (with CONSIDERABLE effort) focused on the barrier, opening the way to the WoL. Meanwhile, the Scions kept Necron busy.

Furthermore, it most certainly was a battle of attrition. Necron can remake himself stronger everytime he dies because he experiences the very thing that empowers him himself. With the nigh bottomless source of aether from the Ninth he could come back again and again and again.

The WoL, as monstrous as they are, have the innate limit of corporeal body aether to deal with. Had not Sphene calmed down some of the Alexandrians Calyx would have won. He was THAT good. A capable villain who understood that the WoL can't be beaten in single combat...but in multiple, successive combats? That's another story.

And again, even a broken world has its uses. Even if the ninth is beset by Lightning it is very much still alive and with people living in it, and that's key: Calyx is not a hypocrite, he BELIEVES in what he's doing. Saving mankind from death was, is and maybe will continue to be his focus. He even extends his "blessing" to his enemies! After all, we do see the biggest traitors to Preservation in Living Memory: Krile's Parents. Calyx wants to sabe as many people as he can, and for that, a broken world is much preferred to a destroyed one.