Yeah, I had a couple tries at the "just survive" strategy. The problem is that those damn Banshees would always trap me in a corner. My strategy became to kill them as quickly as possible and then when everyone else overran my position, I started running around and shooting like a madman. I finally managed to survive. Of course I was on the opposite end of the map from where I needed to be. I was sure I was going to die just trying to get to the missiles but somehow I made it.
Overall I wasn't a fan of the final mission on Earth. It seemed hard for the sake of being hard.