Nope, of course it's not bad, I actually spent an hour just watching them fight Rampant waves and Big Monsters bosses :)))) Stage 4 is truly powerful now, and can actually clear huge hives by itself.
About struggling to kill the hordes, there's a map setting to reduce their number. Making it bigger increases the number of "walkers" that come at a time, but decreasing it means smaller, more manageable waves, so feel free to tweak it to your linking. 0.75 should be the same as the original released version.
About the ammo, while you're right to go for physical weapons against them (only 25% resistance), yellow ammo is a bit weak. I would also suggest farming the pods for research if the bases near you have any. It's much easier than fighting the main base. And another tip: attrition is your friend ;)
Please let me know if you are still struggling, the mod is still in beta and balancing is a bit hard for me knowing how everything works and how to beat them.