Your strategies must be terrible then because they really aren't hard to beat in a coop game. At least one of you should be buying claymores to put down in preparation for that round - claymores are very effective at killing them. You should be running in a consistent direction the whole time to avoid getting surrounded and all you have to do is line them up behind you and fire at them in bursts. The MPL works fine. And you shouldn't need jugg by round 5-7 (spend your points on doors and guns first)

Turns out we'd been doing the same thing as everyone else for the most part. the problem was the person who was hosting, all our pings were fine but for some reason when this certain posted it made things stutter around so you'd be aiming where they weren't.
after swapping our host we've had 0 problems.

Did you even test this properly? (obviously you did, im just being salty)
yeah it's all great and in depth but those fucking special wave enemies are so OP its unreal, they blink everywhere, when they attack you they move inside you so you cant hit them and the colliding hitboxes pushes you away from them, and if you run they just tap your ankle as you go.

i wish i could say me and my mates are just bad, but after 20+ attempts using various strategies, having juggernaut and a variety of weapons, we can rarely beat wave 5-7 (depending on their spawn)

From what we've played so far its fantastic, lots of attention to detail and lots of interesting exploring to do, loving it.
If anyone can shed light onto why we can barely kill these little blighters that'd be grand.