They are not intended for NPC fights. Their damage is scaling depending on player hp, and it seems that for NPCs it just outright kills them in oneshot. That is not a balance issue, just a mechanic

ik their not meant for npc but they would be so much better if i could have em fight other stuff cus ion like fighting things in this wonky source engine game

They can't one shot tanks and helicopters though, along with similar vehicle npcs.

My only complaint about the balance is the accuracy of the oppressors' aiming, they had too much aimbot, as in principle almost all snpc humans on this base. With the new update, it seems that their accuracy is not so high to die in half a second, I hope this will affect the oppressors, the helicopter, the main boss and that thing with the shotgun, they all have this aimbot attack