Am I missing some sort of mathematical simplicity in the elliptical arc specification, because it looks like an absolute mess; surely there must be some mechanism that allows you to specify an elliptical arc between two points using tangent definitions, bezier-style. As it is, there's a real mess there where rotating the end point around the start point, you have to rotate the elliptical axis in the opposite direction to maintain the same curve.

It looks like its one optimal scenario is in creating a rounded corner, which I guess is the common use case - but the unpredictability of how the curve changes if you move the end points without adjusting the corner radii seems to be a significant downside.