That’s what I’m saying, it’s the limited way of drawing curves in Sculpt mode, and it works by projecting the stroke along the curve on the surface. We currently have many ways in Blender to obtain curves with precision on the mesh surfaces, and we should be able to use those curves to sculpt along them, by proximity. This was possible only with an addon, but also with many limitations.
Anyway there are many limitations and things to improve in Sculpt mode, for example those cited in this thread: