The Sketchup object model has a perfectly adequate arc definition that understands correct arc geometry and uses straight facets mostly only for display purposes. Arc geometry is correctly maintained even if arcs are scaled in both x and y, or are split at any point at intersections or for boolean results. But with the offset command the programmer just made a mistake. He could easily have retained arc geometry but just got lazy or didn’t notice.
I could easily write a plugin to do arc offsets one at a time. And users can draw them one at a time. But when using the offset command on a complex face with both straight and arc portions, concave and convex sections, and offset distances that can need some arcs to disappear. it gets a bit mode complicated. The good news is SketchUp already has written the code to do all this, so it should not be that difficult to fix the small part of the code where the mistake about arcs was made.