...Because it has larger mass and inertia, maybe?
The Ares is half bomber. Not bad, but I prefer intercepts.
And the worst weapon? Infyrno. I have yet to hit anything with it, and keep in mind I've detonated them from two meters away from enemy ships, as well as a half dozen other positions. They're simply useless, and all those explosions going exactly the same looks like ****. The Lamprey is a nice idea, it's good to build on by supercharging it in mods, and its little loadout anim kicks ass. Nobody who really wanted to do any damage would pick out a Lamprey, whether they knew much of anything about it or not, because anyone with common sense would realize that you're trying to kill the other guy as quickly as possible, not drain his power reserves, take a minute, and THEN kill him, after a suitable time to get your ass shot off yourself. Thus, it sucks less than some.
I'd have to say, though, for primary weapons the Prometheus R takes the cake, as both useless and high-consumption. Subaches are more dangerous, and don't drain your power within seconds.
A close second would be the Maxim, simply because you can't bloody aim when your ship is doing the can-can.