The curve widget is driving me crazy. I have written a small proposal to fix it on Google Drive:

https://docs.google.com/document/d/1dhUpyHu3uRxUXPMVEhAPTPcjcWLhbzFYmsO5j8_njyA/edit?usp=sharing

Basically the mouse distance threshold to select points is much too small and the spline algorithm never makes the curve I want. My proposal is to increase the selection threshold (to 75-100 pixels) and add a new curve interpolation mode the behaves more like Gimp or Blender's curve widgets.

Thanks!

Please prepare a patch and post it as a merge request on invent.kde.org/graphics/krita.