I don't think anybody would even bother taking the Pirates, with out Grav engines. Speed is what the Pirate is all about. Speed in spreading out and locating everybody, and Speed of getting away with the spoils.
Lots of tactics and ship building and early starting ships, are all based off of Grav engines. Warp1 warpwell, towcapture is all based on the advantage of the Grav Engines of the Pirate. Without the Grav Engines, foes would be set to intercept there own ships, and the Pirate Rob success rate would DROP like a ROCK, and there would be TONS of Pirate ships exploding.
Some people spend an entire lifetime wondering if they made a difference.
The US Marines don't have that problem.
President Ronald Reagan