The clipCircle's precision is 6 degrees (like geoCircle's precision), and the resulting segments are visibly linear on any azimuthal projection's sphere. I would like to make it either configurable (with a default of 6), or to change the value to 2 degrees.
I would also argue that geoCircle's default precision could be set to 2 degrees instead of 6. The trade-offs for speed vs quality might be a bit different 10 years later, with faster computers everywhere.

• geoCircle addressed by default geoCircle precision to 2 degrees #281
• clipAngle addressed by set clipCircle precision to 2 degrees #282