I think you missed the point. Darktable, effectively, has a parametric curve (implemented by the tone mapper) at the end of its processing chain. And this "curve" will, by default, compress contrast at the bright end in a way undesirable for high-key photos (infinitely smooth rolloff instead of sharp clipping). Adding another curve below that will not help, as the contrast compression factor by the tone mapper is gradually approaching infinity. The fight with this default, which is inappropriate for high-key photos, was the topic of my previous comment.

Curves (in the form of Tone Equalizer and the old display-oriented Curve) do exist in Darktable, as well as parametric, drawn, external, and, since 5.6, AI masks.

Another problem with Darktable is, that it has millions functions, demosaic algorithms, sharpening styles, etc. and a lot of developers that probably like tons possibilities but fail incredibly with default options thus making this software inappropriate for photographers that need few reliable tools to get job done rather than experimenting with sliders and buttons.

You speak in theory that geeks and enthusiastic photographers like talk about. Pro photographers don't care, they need results.