Yeah, I'll just push through it until they fix it. I imagine the Koreans are complaining about it too, since my PC isn't a terribly low end one.
For me, playing windows actually helps me more.
I have no idea what's happening over there but perhaps you should try to run the game after a fresh restart of your pc, and take note of any changes you may notice.
It's all the dumb effects that you can't disable that are causing it, especially the fire. It doesn't help that those exploding barrels are everywhere too. I can't even do the area 2 defense map since that damn fire wave keeps happening and cutting the framerate in half. I hope they fix this soon because there's no reason why the game should be slowing down that often for such dumb reasons.