I do not understand. You are saying you spawn in, never move forward (never use right mouse button) and are able to beat the game? You actually spawn in outside the asteroid belt and your laser would only be able to reach a few of the asteroids. So when you are saying the ship feels more nimble, you are just talking about spinning in a circle not actually flying it? haha, I guess I never imagined anyone would try to play it that way or it would even be possible. Without trying it myself, my thought would be that you would hit the few large asteroids that are within range and they would get pushed out of range pretty fast and maybe you could get a couple of zurg asteroids, but not nearly enough to get to 3000.
I did go into the first level again after beating my first run to see how flying around felt after the change. It's better than before. But also yes, just the turning speed itself helps so much in the feel of the game.
It seems to me the best strategy I can find for this game is to never move. I spawn in, shoot all the asteroids I see to break them apart, then shoot all the green zurg asteroids that are floating around everywhere and pass the level. The laser goes quite far and I can hit most asteroids I can see without moving. Moving is just a waste of fuel and inefficient.