Jerk is defined as change in acceleration. The greater the change the more jerk. The bar itself does not indicate jerk but quick and large changes in the regen bar do indicate jerk.
Yes.
You want to see a nice, reasonably gradual increase to a peak (it by necessity can be quick, but a nice smooth, but rapid, increase is good rather than a jolt), then a linear decrease (display is likely not linear though) as speed slows, if you want uniform deceleration. Uniform deceleration means linearly decreasing stopping power (F*v).
In practice, often deceleration can and should be lowered gradually (makes it easy to avoid jerk at the end), so the drop in stopping power may be faster than linear.
The issue, as you have pointed out, is the jumpiness. Inherently, a certain amount of stopping power is required. The integral over time of this stopping power has to be roughly the same in all cases (neglecting wind resistance, etc.).
So when we see a sudden spike, followed by a period of minimal regen, we know that some of that high regen could have been redistributed to other times to make the integral the same - but with lower jerk (less rapid changing of the regen bar length). Just a nicer, more consistent (constant), reassuring stopping force.
(Of course, there are limits to allowed regen at different speeds, at least when driving manually. I don’t know whether adjustments are made to these limits for FSD. But my point is that there are limits at lower speed, so you do need to make sure to take advantage of the available stopping power all the down.)
where regen is higher when slowing downhill.
It has little to do with the length of the regen bar. Large amounts of regen are fine. It has to do with how it gets to that peak, and how the length is reduced all the way to a stop.
You can see this in the video of me driving, posted earlier, but I’ll post more examples for side-by-side comparison.
It seems like you have a certain exact preference for decel / accel / aggressiveness that fsd beta isn't meeting.
It’s actually a very common complaint; from the survey it seems likely that more than half the people with Beta are likely annoyed by this.
It’s not an exact preference. Some braking even is ok, if someone likes really fast stops! But it should be done smoothly. Maybe I can post an example of that too (except unfortunately the display does not show braking when driving manually so it is hard to see what is happening).