Thank you all.
I often wonder about these things because airliners do seem to be more stable than the light aircraft I fly (a TB20).
Yet the only differences I can see are the much higher wing loading on jets, and their yaw damper.
I know wing loading makes a big difference - the TB20 is a lot more stable in turbulence than most other light aircraft as a result. But there are very few with a YD fitted and I have not found anybody with an experience on the same type with and without a YD. A YD should help because it blocks the yaw which is a side effect of the constant roll axis corrections which one gets when on autopilot.