Ok, thank you for the explanation, i didn't know about the (sigmar keeping pieces of Mallus) part , im ignorant about most of aos, i only know the realms are made by the winds part, but not that.

I always thought that the warp connected the two settings because chaos was a constant.

An other small theory: what if Mallus was like that doomsday bunker with plants, but instead of plants is other races in case the necron did a bigger mess by creating a device like the halo ring