piece of advice when playing this game; be careful playing the factory/foundry on hard. i just played most of it and it actually made me hate the game with the amount of Zs and mutants swarming you; i had to use an auto-clicker at one point just to thin the bastards out, it was that godawful.
I believe that's the very definition of "ass-holey game design" where instead of making the enemies challenging in any meaningful way, just spam swarms of them, and throw in the odd mutie to boot. this shit turns SOD2 into a war of attrition; which will give out first? the horde, or your hand when you get carpal tunnel
Edit: i just realised after posting this that it might not be JUST that level, be careful all-together.