My instinct tells me there’s logic to the fact that simply turning on points on a pline provides a means to edit an arc (of a consistent radius) into another arc (with another consistent radius). I can pull on all 3 points and make a parabola. I can pull on the centre point and make a pointed arch. Pulling on a side point turns that side into a subarc.
There are two things I’m wondering:

How to simply change the radius of an arc segment  which stays an arc while maintaining the position of its starting and ending points.

What’s the advantage of so easily enabling the irregular deformation of an arc rather than easily enabling the retention of its consistent radius? Seems to me most CAD packages have it the other way around.