I already know curves are actually segments. Zooming in you can see that as well. Same for a curved wall.

But it looks like I have to set an artificial limit like 1000 or 5000 to avoid processing of too many points and generating a huge SVG cutout string. The generating itself works amazingly well and is very fast in both C# and PHP. It even works with other objects like a wall. The Sweet Home 3D exports are perfectly formatted for this.