It's a pity that Fit Curve > Fit Spline doesn't accept an edge as the source.
To simplify an edge, I attempt to use Extract Geometry > Composite Curve > Advanced Curve Fit > Degree and Segment.
But as shown below, when I set Degree = 2 and Segments = 1, what I get is Degree = 2 and Segments = 5.
Do I misunderstand how Advanced Curve Fit works? Thanks!