Just got my ass kicked by 200 shamblers

Randy was merciful enough to split them in two groups, but while my fighters dealt with the first, the second wrecked my whole base, beat up the kids, the mechanoids, tore the walls of the containment chamber and now i have a loose revenant, one of the doctors was ambushed and killed while rescuing someone and the hussar died fighting. all my walls are breached. my animals are running lose. I have a high end industrial colony with excellent chain shotguns and flak, and vampires running around in cataphract with persona weapons. How. Why. There are corpses everywhere. dear fucking god. how are these worse than all the biotech fights?