An interesting problem. Like you say, it's as if it is drawing a number of linked straight lines.
53% is on the high side for Pulled string. How big is your canvas? Try turning on rulers (Ctrl r) and set them to pixels (right click inside the ruler). Using your brush size as a rough guide, and the same brush settings, you can see that the pulled string radius is HUGE

If I change direction with those settings, I get a sharp corner because the length of the pulled string is longer than the radius of the curve I am attempting to draw.

I get much better results using Stroke Catch-up with much lower smoothing.

It does not appear to be the case from your screen shots, but snapping to grid or guides can distort brush strokes by pulling the stroke off course.