When there's something like mortality, there is a dev server, no? Besides, the invader units were overpowered. That is something that should have been tested out before mortality was activated as well.
Testing massive battles in realistic situations on the dev server is vastly easier said than done.
I mean, sure, we could gather together all the troops of 2 or 3 realms in a single region and dump thousands and thousands of Daimons in the region with them, and watch what happens.
But that will not tell us
anything about how overpowered they are, because that depends extremely strongly on just how good the humans are at banding together and getting their forces in the same place at the same time.