I have never seen stats showing that FSD is "rapidly improving". Quite the contrary, it seems hobbled by its backward hardware and plateaued in terms of progress.
The backward hardware in my 2020 car has plateaued at driving me driveway-to-parking-lot on 100% of my drives in recent history. It’s a pretty nice plateau, really.
(I admit I’m mocking your wording; in fact it has not plateaued. Just every update makes things slightly smoother in non-safety-critical ways.)