Have you plans to rebalance the difficulty levels? 1-3 is pretty easy and then the jump to 4 is really big. I have several friends that clear 3 super easy and it's boring for them but they get overwhelmed almost every mission on 4.
Sometimes I have the feeling on 3 there are 10-20 bugs per swarm and on 4 there are coming hundreds.
I don't think you should lower the difficulty of 4 but the jump from 3 to 4 is too big.
No plans to re-balance the haz levels but perhaps we can find another way to give players more fine control over the games difficulty.