our quick assumption, or at least mine, has been that The Battleplain was such an epic battle that it created a topos.
Well that doesn't scan, otherwise most major battles or other tragedies would have a topos potential, and they seem to have not created one, 200,000 people died in the desert on the way to the Circumfix, but no topos in the desert (presumably).
What is unique to Mengedda, most likely, is that the death of the No-God released all the suffering that was contained/fueling him. Perhaps the no-god was an attempt to contain or weaponize a topos. Because if you can ensnare Hell itself in a ghostbuster Ecto-Containment Unit/Ghost Trap you may just have solved the problem of Hell.
Unfortunately, this may have caused all the supposed suffering because it also proved that everybody is already always damned/going to hell anyway. And cutting off people's connection to hell meant their soul had no where to go when it died or it meant that souls trying to leave hell had no where to go when they're born--or if you're predestined, if a soul is already damned before it is conceived/born/created, but there is no longer a mechanism for the damnation to take effect then one can't be conceived/born and if the automatic damnation of a soul is a crucial precondition to a soul's existence then a new soul cannot come into existence.
In other words, perhaps damnation is so crucial to the human experience that to be severed from damnation is to have no existence. To be human is to be damned. (and perhaps humans were only created so that they could be damned by the gods, much like we raise cattle to harvest them and feast on their milk and flesh).