Sheesh
This was the result of the Nids coming when we had Centuries in advance of warning, All-XX, a three-nation alliance that turned to a Four-Nation-Alliance when the Aeldari joined last minute, and with all our best weapons at the time that are non-esoteric, esoteric, and super-esoteric. With worlds prepped for maximum "Fuck You" to the Bugs.
And even then it sounds like we are just barely holding them back. With only this Aethyr calculant's "Sick as Hell Heresey (TM)" being are best, if not, only weapon left above psychically sundering thirteen-thousand light years bellow us. Hope the Seyfert survived.