Interesting, that would confirm the pressure advance as the likely culprit (speed and acceleration are taken into account in the algo). Maybe your slicer has a bug related to this? If changing the value wildly does not improve or worsen it, then it might not be calculating what it’s supposed to. Can you try another slicer?

All seems to indicate something related to pressure advance, whereby the printer thinks it needs to extrude less because of some pressure buildup but it underestimates how much is really needed. Does it happen if you print slowly? E.g max 15 mm/s or less.

Have you seen how fast printers with stepper motors can get? They print benchies in less than 3 minutes. The bottleneck is not the motion system, it’s either the hot-end or the part cooling. Also stepper are super accurate and very flexible. Drivers are advanced and can tune for torque, speed, sound etc. Collision detection and skipped step detection is also a thing.