Author here. I did not say circles don't draw well. I said that "swiftly-drawn curves are flattened" and likened it to a "large wash." By that I mean long, swift, edge-to-edge brush strokes. Perhaps the use of the word "curves" confused that point, but the natural arcs of human hand/wrist motion are what I wanted to evoke. I also noted a "fat brush in symmetry mode" exhibits the same effect. I can attest to two points about that from firsthand experience:

1. That was also true on original hardware (when I owned the system in my younger days). I distinctly remember having to slow down certain movements to let the system keep pace, depending on speed and complexity of motion. 2. The effect is drastically improved (and I note so in the article) by choosing a faster virtual CPU.