As a general rule, thrust rotation rates are based on the shape of a ship. A ship that is very short and wide (like the cobra or T9) will yaw terribly; a ship that is very tall for its length (like a T7) will have comparatively good yaw.
The in-game reason for this is the placing of thethrusters on a ship. Take the Asp, or Cobra, or Sidewinder even; go into external view and watch which thrusters fire when you roll, pitch and yaw. It's got thrusters pointing in the roll and pitch directions, but for yawing, there aren't any sideways-mounted thrusters, it has to fire pairs of thrusters at angles, which is horribly inefficient. To get good yawing, you need sideways-mounted thrusters - ideally, a vertical wall to mount such thrusters on.
This leads to a logical question: why are most ED ships so horribly designed, such that they don't have any sideways-mounted thrusters?
The answer is simple: it is a deliberate game design decision. The original Elite game, back in the 1980s, only had controls for pitch and roll - there were no yaw controls (or if there were, I never found them on the Commodore 64). Everyone had to learn to fly their spaceships - and aim their non-gimballed weaponry at targets just a couple of pixels wide - using just roll and pitch. We all had to "git gud" at it.
As the spiritual descendant of that ancient game, the designers of ED have elected to continue that preeminence-of-pitch-and-roll ethos as a core design decision. As a result, all of the spaceships in ED are deliberately designed to yaw badly. The few that don't (such as the T7) are really poor at maneuvering overall; rather than having good yaw, they've simply got pitch and roll that are as poor as the yaw on other ships.